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Terminal duct––lobular unit (TDLU). Terminal duct lobular unit (TDLU). AA, ,

Diagrammatic representation of this structure. Diagrammatic representation of this structure.

terminal duct; ITD = Extralobular terminal duct; ITD = ETD = Extralobular ETD = terminal duct. intralobular terminal duct. intralobular

Mammary gland Mammary gland

Mammary gland Mammary gland

Terminal duct––lobular unit (TDLU). Terminal duct lobular unit (TDLU). BB, ,

Photomicrograph of this unit as seen in a normal Photomicrograph of this unit as seen in a normal adult female. adult female.

Mammary gland Mammary gland

Mammary gland Mammary gland

Immunocytochemical markers of mammary markers of mammary Immunocytochemical in positivity in , showing positivity Lactalbumin, showing lobule. AA, , Lactalbumin lobule. lumina. . intraglandular lumina secretory epithelium and secretory epithelium and intraglandular

, showing positivity

markers of mammary lobule. BB, , Immunocytochemical markers of mammary lobule. Immunocytochemical cell myoepithelial cell positivity in the outer ActinActin, showing in the outer myoepithelial component. Smooth muscle cells present in adjacent component. Smooth muscle cells present in adjacent in controls. vessel walls serve as built--in controls. vessel walls serve as built

changes in mammary lobule. There is Lactational changes in mammary lobule. There is Lactational

marked cytoplasmic marked vacuolization. cytoplasmic vacuolization.

related Cystic involution of lobule. This is an age--related Cystic involution of lobule. This is an age change of no clinical significance. change of no clinical significance.

AA, Pregnancy like changes in mammary lobule. , Pregnancy--like changes in mammary lobule. These two clinically inconsequential alterations These two clinically inconsequential alterations may coexist. may coexist.

BB, Clear cell changes. These two clinically , Clear cell changes. These two clinically inconsequential alterations may coexist. inconsequential alterations may coexist.

ectasia. . Gross appearance of mammary duct ectasia Gross appearance of mammary duct Some of the dilated ducts contain a thick dark Some of the dilated ducts contain a thick dark material. material.

traumatic fat necrosis involving breast. PostPost--traumatic fat necrosis involving breast.

Retraction of skin in a patient with fat necrosis Retraction of skin in a patient with fat necrosis (arrow), as seen in a photograph taken from a (arrow), as seen in a photograph taken from a seasoned paper. wellwell--seasoned paper.

mastitis in a diabetic lymphocytic mastitis in a diabetic Sclerosing lymphocytic Sclerosing woman. Some of the lymphocytes infiltrate the woman. Some of the lymphocytes infiltrate the gland. gland.

granulomatous reaction to silicone. Foamy reaction to silicone. Foamy Florid granulomatous Florid type multinucleated macrophages, foreign body--type multinucleated macrophages, foreign body giant cells, and lymphocytes are present. giant cells, and lymphocytes are present.

. The lesion is fibroadenoma. The lesion is Gross appearance of fibroadenoma Gross appearance of sharply circumscribed and perfectly round, and it sharply circumscribed and perfectly round, and it contains numerous slits. contains numerous slits.

. The fibroadenoma. The

Microscopic appearance of fibroadenoma Microscopic appearance of hypercellular has a slightly hypercellular tumor shown in BB has a slightly tumor shown in but not to a degree that would justify a stroma but not to a degree that would justify a stroma diagnosis of phyllodes diagnosis of tumor. phyllodes tumor.

. The fibroadenoma. The

Microscopic appearance of fibroadenoma Microscopic appearance of hypercellular has a slightly hypercellular tumor shown in BB has a slightly tumor shown in but not to a degree that would justify a stroma but not to a degree that would justify a stroma diagnosis of phyllodes diagnosis of tumor. phyllodes tumor.

Heavy, coarse calcification in a large breast Heavy, coarse calcification in a large breast as seen in a mammogram. fibroadenoma as seen in a mammogram. fibroadenoma

Fibroadenoma with with apocrine Fibroadenoma

metaplasia. . AA, ,

apocrine metaplasia eosin section showing a prominent Hematoxylin––eosin section showing a prominent Hematoxylin

cells at the eosinophilic cells at the discontinuous layer of plump eosinophilic discontinuous layer of plump base of the gland. These should not be confused with base of the gland. These should not be confused with cells. neuroendocrine cells. neuroendocrine

metaplasia. . BB, ,

Fibroadenoma with with apocrine Fibroadenoma Immunostain for GCDFP Immunostain apocrine metaplasia for GCDFP--15. 15.

Giant fibroadenoma Giant

occurring in an adolescent fibroadenoma occurring in an adolescent female. female.

with focal involvement by low-- Fibroadenoma with focal involvement by low Fibroadenoma carcinoma. intraductal carcinoma. grade intraductal grade

Gross appearance of lactating adenoma. The Gross appearance of lactating adenoma. The mass has a distinct lobular configuration, mass has a distinct lobular configuration, yellowish color, and marked vascularization yellowish color, and marked vascularization. .

SoSo--called called ““lactating adenoma. lobules show marked cytoplasmic lobules show marked lactating adenoma.”” The The hyperplastic hyperplastic vacuolization. cytoplasmic vacuolization.

intraductal papilloma

. A papilloma. A Gross appearance of intraductal Gross appearance of mass is seen protruding within the polypoid mass is seen protruding within the polypoid lumen of a markedly dilated duct. lumen of a markedly dilated duct.

Intraductal papilloma Intraductal showing complex arborizing showing complex power appearance papilloma. . AA, Low, Low--power appearance architecture. arborizing architecture.

Intraductal papilloma Intraductal power view , High--power view

papilloma. . BB, High defined showing dual cell composition, with a well--defined showing dual cell composition, with a well row of myoepithelial row of cells. myoepithelial cells.

Gross appearance of papilloma Gross appearance of presenting as a papilloma presenting as a

mural nodule within a cyst. mural nodule within a cyst.

of breast showing entrapment of Papilloma of breast showing entrapment of Papilloma stroma, , fibrohyaline stroma epithelial structures by fibrohyaline epithelial structures by appearance. pseudoinvasive appearance. resulting in a pseudoinvasive resulting in a

Typical polypoid Typical shape of nipple adenoma, as polypoid shape of nipple adenoma, as

seen in a whole mount. seen in a whole mount.

Nipple adenoma. The complex architectural Nipple adenoma. The complex architectural . The overdiagnosis. The arrangement can lead to overdiagnosis arrangement can lead to epithelium of the squamous epithelium of the continuity with the squamous continuity with the

skin is a typical feature of this entity. skin is a typical feature of this entity.

power view. The adenosis. . AA, Low, Low--power view. The Sclerosing adenosis Sclerosing lobular configuration of the lesion is obvious. lobular configuration of the lesion is obvious.

Sclerosing adenosis Sclerosing power view. , Medium--power view.

adenosis. . BB, Medium Note the spindle shape of the proliferating cells in Note the spindle shape of the proliferating cells in quality of fibrillary quality of the center of the lobule and the fibrillary the center of the lobule and the nature. myoepithelial nature. the cytoplasm, indicative of myoepithelial the cytoplasm, indicative of

Sclerosing adenosis Sclerosing

stain for actinactin showing strong stain for adenosis. . CC, , Immunocytochemical Immunocytochemical showing strong immunoreactivity in immunoreactivity in

the myoepithelial the cell component. myoepithelial cell component.

Sclerosing adenosis Sclerosing adenosis. . DD, , Sclerosing Sclerosing adenosis adenosis with with

lobular carcinoma in situ. Note the regularity of lobular carcinoma in situ. Note the regularity of the edge and absence of infiltrative features. the edge and absence of infiltrative features.

Benign ““perineurial Benign perineurial invasion in a breast lesion invasion”” in a breast lesion

that had elsewhere the typical features of that had elsewhere the typical features of sclerosing adenosis sclerosing adenosis. .

Involvement of the wall of a vessel by sclerosing sclerosing Involvement of the wall of a vessel by van Verhoeff––van adenosis, as highlighted by the adenosis , as highlighted by the Verhoeff

stain. Gieson stain. Gieson

power hyperplasia. AA, Low, Low--power Microglandular hyperplasia. Microglandular appearance, showing haphazardly scattered appearance, showing haphazardly scattered small round glands. small round glands.

Microglandular hyperplasia. Microglandular , On high power, hyperplasia. BB, On high power,

the glands are open and contain a luminal the glands are open and contain a luminal cell layer is not myoepithelial cell layer is not secretion. The myoepithelial secretion. The discernible. discernible.

Adenomyoepithelial adenosis Adenomyoepithelial large, with a wide, open lumen and apocrine large, with a wide, open lumen and

. The glands are relatively adenosis. The glands are relatively metaplasia. . apocrine metaplasia

The cellular component in between is composed of The cellular component in between is composed of

myoepithelial cells. myoepithelial prominent myoepithelial prominent

100 Protein stain highlights the cells. BB, S, S--100 Protein stain highlights the component. myoepithelial component.

Adenomyoepithelial adenosis Adenomyoepithelial large, with a wide, open lumen and apocrine large, with a wide, open lumen and

. The glands are relatively adenosis. The glands are relatively metaplasia. . apocrine metaplasia

The cellular component in between is composed of The cellular component in between is composed of

myoepithelial cells. myoepithelial prominent myoepithelial prominent

100 Protein stain highlights the cells. BB, S, S--100 Protein stain highlights the component. myoepithelial component.

Fibrocystic changes, including cystic dilatation, Fibrocystic changes, including cystic dilatation, hyperplasia, ductal hyperplasia, apocrine metaplasia apocrine metaplasia, florid , florid ductal

and fibrosis. and fibrosis.

hyperplasia. There is ductal hyperplasia. There is Photomicrograph demonstrating florid ductal Photomicrograph demonstrating florid no evidence of necrosis, and individual cells are well supported by by no evidence of necrosis, and individual cells are well supported their stroma . A prominent cleft has formed between a solid stroma. A prominent cleft has formed between a solid their intraluminal proliferation and an outer epithelial row. This feature proliferation and an outer epithelial row. This feature intraluminal is usually indicative of a benign condition. is usually indicative of a benign condition.

hyperplasia. Note the oval shape of ductal hyperplasia. Note the oval shape of Florid ductal Florid the nuclei and the parallel arrangement, resulting the nuclei and the parallel arrangement, resulting

in a ““streaming in a effect. streaming”” effect.

Structure resembling a renal glomerulus Structure resembling a renal in florid glomerulus in florid

hyperplasia. ductal hyperplasia. ductal

hyperplasia showing irregularly shaped Ductal hyperplasia showing irregularly shaped Ductal ridges connecting opposite portions of the wall. ridges connecting opposite portions of the wall. Note the fact that the oval nuclei are arranged Note the fact that the oval nuclei are arranged parallel to the long axis of the ridge. parallel to the long axis of the ridge.

. The cylinders have a spherulosis. The cylinders have a Collagenous spherulosis Collagenous round shape and a homogeneous pink staining round shape and a homogeneous pink staining quality, consistent with basement membrane quality, consistent with basement membrane material. material.

Gross appearance of radial scar. Gross appearance of radial scar.

Typical stellate Typical shape of radial scar as seen on stellate shape of radial scar as seen on

low power. low power.

Abundant deposition of elastic tissue in the Abundant deposition of elastic tissue in the central portion of a radial scar, as highlighted by central portion of a radial scar, as highlighted by

the Verhoeff the Verhoeff––van van Gieson stain. Gieson stain.

AA, Benign , Benign ductular structures entrapped in radial ductular structures entrapped in radial

scar. Note their regular contour and the scar. Note their regular contour and the stroma. . hyaline quality of the stroma hypocellular hyaline quality of the hypocellular

BB, Tubular carcinoma shown for comparison. , Tubular carcinoma shown for comparison. Note the angulated shape of the glands and the Note the angulated shape of the glands and the desmoplastic stroma desmoplastic stroma. .

intraductal grade intraductal

Radial scar with associated low--grade Radial scar with associated low carcinoma. carcinoma.

intraductal grade intraductal

Radial scar with associated low--grade Radial scar with associated low carcinoma. carcinoma.

Two different breast lesions diagnosed as atypical Two different breast lesions diagnosed as atypical lobular hyperplasia by four experts in breast pathology. lobular hyperplasia by four experts in breast pathology. There is lobular enlargement and proliferation, but some There is lobular enlargement and proliferation, but some are preserved, and there is only minimal lumina are preserved, and there is only minimal lumina distention of individual units. distention of individual units.

Two different breast lesions diagnosed as atypical Two different breast lesions diagnosed as atypical lobular hyperplasia by four experts in breast pathology. lobular hyperplasia by four experts in breast pathology. There is lobular enlargement and proliferation, but some There is lobular enlargement and proliferation, but some are preserved, and there is only minimal lumina are preserved, and there is only minimal lumina distention of individual units. distention of individual units.

ductal Two different breast lesions diagnosed as atypical ductal Two different breast lesions diagnosed as atypical hyperplasia by two experts in breast pathology. There is hyperplasia by two experts in breast pathology. There is type ductal type marked epithelial proliferation in structures of ductal marked epithelial proliferation in structures of

associated with atypia associated with

, but they were felt not to fulfill atypia, but they were felt not to fulfill

criteria for carcinoma in situ. criteria for carcinoma in situ.

ductal Two different breast lesions diagnosed as atypical ductal Two different breast lesions diagnosed as atypical hyperplasia by two experts in breast pathology. There is hyperplasia by two experts in breast pathology. There is type ductal type marked epithelial proliferation in structures of ductal marked epithelial proliferation in structures of

associated with atypia associated with

, but they were felt not to fulfill atypia, but they were felt not to fulfill

criteria for carcinoma in situ. criteria for carcinoma in situ.

ductal lesion diagnosed as atypical Proliferative ductal lesion diagnosed as atypical Proliferative hyperplasia on account of the ductal hyperplasia on account of the ductal features and small size. cytoarchitectural features and small size. cytoarchitectural

ductal lesion diagnosed as atypical Proliferative ductal lesion diagnosed as atypical Proliferative hyperplasia on account of the ductal hyperplasia on account of the ductal features and small size. cytoarchitectural features and small size. cytoarchitectural

Flat epithelial atypia Flat epithelial . The spaces are dilated and atypia. The spaces are dilated and

lined by columnar epithelium showing scanty lined by columnar epithelium showing scanty atypia. . atypia

power area of calcification LowLow--power area of calcification

HighHigh--power views of the corresponding power views of the corresponding microscopic specimen. microscopic specimen.

Specimen from a fine needle aspiration (FNA) biopsy. Specimen from a fine needle aspiration (FNA) biopsy. This was diagnosed as breast carcinoma and followed This was diagnosed as breast carcinoma and followed by the performance of a mastectomy, which confirmed by the performance of a mastectomy, which confirmed

the cytologic the

interpretation. cytologic interpretation.

features of various types of breast Cytologic features of various types of breast Cytologic lesions as seen in FNA specimens: AA, , lesions as seen in FNA specimens: fibroadenoma. . fibroadenoma

Cytologic features of various types of breast features of various types of breast Cytologic apocrine lesions as seen in FNA specimens: BB, , apocrine lesions as seen in FNA specimens: metaplasia. . metaplasia

Cytologic features of various types of breast features of various types of breast Cytologic , invasive lesions as seen in FNA specimens: CC, invasive lesions as seen in FNA specimens: carcinoma. ductal carcinoma. ductal

Cytologic features of various types of breast features of various types of breast Cytologic , invasive lesions as seen in FNA specimens: DD, invasive lesions as seen in FNA specimens: carcinoma. ductal carcinoma. ductal

Cytologic features of various types of breast features of various types of breast Cytologic medullary lesions as seen in FNA specimens: EE, , medullary lesions as seen in FNA specimens: carcinoma. carcinoma.

Cytologic features of various types of breast features of various types of breast Cytologic mucinous lesions as seen in FNA specimens: FF, , mucinous lesions as seen in FNA specimens: carcinoma. carcinoma.

Cytologic features of various types of breast features of various types of breast Cytologic , invasive lesions as seen in FNA specimens: GG, invasive lesions as seen in FNA specimens: lobular carcinoma. lobular carcinoma.

Biopsy--induced Biopsy induced artifactual artifactual changes: , tumor changes: AA, tumor

cells along needle tract. cells along needle tract.

Biopsy--induced Biopsy artifactual changes: , tumor changes: BB, tumor

induced artifactual cells in lumen of lymph vessel. cells in lumen of lymph vessel.

Biopsy--induced Biopsy induced artifactual artifactual changes: , tumor changes: CC, tumor

cells in lumen of artery. cells in lumen of artery.

In situ ductal In situ ductal carcinoma with carcinoma with comedo type comedo--type

necrosis. necrosis.

Preservation of a myoepithelial Preservation of a grade intraductal grade

myoepithelial cell layer in high cell layer in high-- carcinoma. (Smooth muscle intraductal carcinoma. (Smooth muscle immunostain) ) actinactin immunostain

Invasive ductal Invasive extensive intraductal extensive ductal carcinoma associated with carcinoma associated with carcinoma component. intraductal carcinoma component.

Intracystic carcinoma of the breast. The papillary carcinoma of the breast. The papillary Intracystic configuration of the tumor is already grossly configuration of the tumor is already grossly evident. evident.

HighHigh--power view of an in situ papillary carcinoma. power view of an in situ papillary carcinoma. Note the layering of cells, loss of nuclear polarity, Note the layering of cells, loss of nuclear polarity,

marked hyperchromasia marked

, and lack of a hyperchromasia, and lack of a cell layer. myoepithelial cell layer. myoepithelial

In situ papillary carcinoma. The arborizing nature arborizing nature In situ papillary carcinoma. The core are fibrovascular core are of this tumor and the stout fibrovascular of this tumor and the stout papilloma. . not too different from those of a benign papilloma not too different from those of a benign

called ““globoid

clear globoid”” or or ““clear for immunoreactive for

These cells, which are immunoreactive myoepithelial 15, should not be confused with myoepithelial

Papillary carcinoma with so--called Papillary carcinoma with so cells.”” These cells, which are cells. GCDFP--15, should not be confused with GCDFP cells. BB, Negative cells.

immunostain for smooth muscle

, Negative immunostain

for smooth muscle actinactin. .

called ““globoid

clear globoid”” or or ““clear for immunoreactive for

These cells, which are immunoreactive myoepithelial 15, should not be confused with myoepithelial

Papillary carcinoma with so--called Papillary carcinoma with so cells.”” These cells, which are cells. GCDFP--15, should not be confused with GCDFP cells. BB, Negative cells.

immunostain for smooth muscle

, Negative immunostain

for smooth muscle actinactin. .

Solid type of in situ ductal Solid type of in situ

ductal carcinoma. There is no carcinoma. There is no necrosis. necrosis.

LowLow--grade in situ grade in situ ductal ductal carcinoma of cribriform carcinoma of cribriform

type. type.

bars in intraductal

carcinoma. Note intraductal carcinoma. Note Trabecular bars in Trabecular the perpendicular arrangement of the nuclei in the perpendicular arrangement of the nuclei in relation to the long axis of the bars. relation to the long axis of the bars.

carcinoma of breast. Some of the Micropapillary carcinoma of breast. Some of the Micropapillary

papillae lack a central fibrovascular papillae lack a central core. fibrovascular core.

Ductal carcinoma in situ of so Ductal

carcinoma in situ of so--called

called ““clinging type.

clinging type.”” One One

or two layers of atypical cells line dilated glandular or two layers of atypical cells line dilated glandular

structures containing granular intraluminal structures containing granular

material in intraluminal material in

which ghosts of tumor cells are identified. which ghosts of tumor cells are identified.

called ““lobular

lobular cancerization

The lobule is markedly cancerization..”” The lobule is markedly SoSo--called expanded and composed of relatively large tumor cells expanded and composed of relatively large tumor cells type carcinoma. Typical ductal--type carcinoma. Typical with the appearance of ductal with the appearance of

carcinoma was present elsewhere in the ductal carcinoma was present elsewhere in the ductal specimen. specimen.

Apocrine variant of in situ Apocrine variant of in situ ductal carcinoma. ductal carcinoma.

Endocrine--type Endocrine carcinoma in situ: AA, ,

ductal carcinoma in situ: type ductal eosin. hematoxylin––eosin. hematoxylin

Endocrine--type Endocrine type ductal ductal carcinoma in situ: carcinoma in situ: BB, ,

chromogranin. . chromogranin

Typical pattern of involvement of terminal duct–– Typical pattern of involvement of terminal duct lobular unit by lobular carcinoma in situ. lobular unit by lobular carcinoma in situ.

Marked expansion of a lobular unit by lobular Marked expansion of a lobular unit by lobular carcinoma in situ. A few small spaces are still carcinoma in situ. A few small spaces are still present in the smaller focus. present in the smaller focus.

Involvement of duct by lobular carcinoma in situ. Involvement of duct by lobular carcinoma in situ. In the presence of such change, a thorough In the presence of such change, a thorough search for typical areas of lobular involvement search for typical areas of lobular involvement should be undertaken. should be undertaken.

carcinoma. ductal carcinoma. Typical gross appearance of invasive ductal Typical gross appearance of invasive like) shape of the tumor, white Note the irregular (crab--like) shape of the tumor, white Note the irregular (crab fibrous appearance, and chalky streaks. Retraction of fibrous appearance, and chalky streaks. Retraction of the overlying skin is obvious in the specimen shown in the overlying skin is obvious in the specimen shown in BB. .

carcinoma. ductal carcinoma. Typical gross appearance of invasive ductal Typical gross appearance of invasive like) shape of the tumor, white Note the irregular (crab--like) shape of the tumor, white Note the irregular (crab fibrous appearance, and chalky streaks. Retraction of fibrous appearance, and chalky streaks. Retraction of the overlying skin is obvious in the specimen shown in the overlying skin is obvious in the specimen shown in BB. .

AA, Gross appearance of typical invasive

, Gross appearance of typical invasive ductal ductal carcinoma. ““Chalky streaks carcinoma. can be seen Chalky streaks”” can be seen

throughout the tumor. A central space can be throughout the tumor. A central space can be identified in some of them (arrows). identified in some of them (arrows).

, Elastic tissue stain of the lesion illustrated in A BB, Elastic tissue stain of the lesion illustrated in A

correspond to a markedly chalky streaks”” correspond to a markedly ducts neoplastic ducts

showing that ““chalky streaks showing that thickened elastic layer in the wall of non--neoplastic thickened elastic layer in the wall of non Gieson) ) van Gieson

crossing the tumor. (BB, , Verhoeff crossing the tumor. (

Verhoeff––van

Prototypical invasive ductal Prototypical invasive carcinoma. ductal carcinoma.

Vascular invasion by breast carcinoma Vascular invasion by breast carcinoma

demonstrated by positivity demonstrated by

of endothelial cells for positivity of endothelial cells for lectin I. I. europaeus lectin UlexUlex europaeus

Tubular carcinoma of breast. The angulated Tubular carcinoma of breast. The angulated

shape of the glands and the cellular stroma shape of the glands and the cellular stroma are are

characteristic of this lesion. characteristic of this lesion.

Invasive cribriform Invasive carcinoma. Some of the cribriform carcinoma. Some of the

nodules have a predominantly solid appearance. nodules have a predominantly solid appearance.

Typical gelatinous gross appearance of pure Typical gelatinous gross appearance of pure carcinoma. Note the sharply mucinous carcinoma. Note the sharply mucinous circumscribed quality of the tumor. circumscribed quality of the tumor.

carcinoma of the breast. Clusters of Mucinous carcinoma of the breast. Clusters of Mucinous differentiated tumor cells are seen floating in wellwell--differentiated tumor cells are seen floating in a sea of mucinmucin. . a sea of

Argyrophilic cells present in another case of mucinous carcinoma of the breast, indicative of neuroendocrine differentiation. (Sevier–Munger stain)

Early form of mucin-producing low-grade carcinoma showing the mechanism of formation of the epithelial strips typically seen floating in the mucin.

Gross appearance of medullary carcinoma. Note the well-circumscribed character and fleshy appearance.

Gross appearance of medullary carcinoma. Note the well-circumscribed character and fleshy appearance.

Medullary carcinoma. The large tumor cells grow in a “syncytial” fashion and are sharply separated from the surrounding stroma, which is heavily infiltrated by lymphocytes and plasma cells.

Gross appearance of secretory carcinoma. The tumor is well circumscribed and shows a variegated cut surface.

Secretory carcinoma. The small uniform glands are filled by a secretory material.

Breast carcinoma with neuroendocrine

differentiation (so-called “carcinoid tumor of breast”).

Strong reactivity for chromogranin in breast carcinoma with neuroendocrine differentiation.

Gross appearance of metaplastic carcinoma. A large, fleshy mass is seen protruding inside a cavity. Microscopically, this tumor showed an admixture of squamous and spindle elements.

Metaplastic carcinoma. The tumor shown in A exhibits a blending of the carcinomatous and sarcoma-like components, whereas that depicted in B has a biphasic (“carcinosarcomatous”) appearance.

Metaplastic carcinoma. The tumor shown in A exhibits a blending of the carcinomatous and sarcoma-like components, whereas that depicted in B has a biphasic (“carcinosarcomatous”) appearance.

Large tumor embolus in a dermal lymph vessel in a case with the clinical appearance of inflammatory carcinoma.

Eczema-like hyperemic and eroded clinical appearance of Paget’s disease.

Low-power views of Paget’s disease. The cleft- like separation between the tumor cells and the overlying squamous epithelium is characteristic.

High-power views of Paget’s disease. The cleft-

like separation between the tumor cells and the overlying squamous epithelium is characteristic.

Melanin colonization in breast carcinoma as seen with argentaffin stain.

Immunohistochemical demonstration of malignant intraepithelial cells in Paget’s disease: A, EMA immunostain.

Immunohistochemical demonstration of malignant intraepithelial cells in Paget’s disease: B, HER2/neu immunostain.

Biopsy of nipple showing scattered clear cells in the basal layer (“Toker’s cells”). These cells show a mild degree of nuclear atypia and were immunohistochemically similar to the cells of Paget’s disease.

Invasive lobular carcinoma. The tumor cells are small and uniform with round nuclei and grow in an Indian file fashion.

Typical target-like growth of tumor cells around an uninvolved duct in invasive lobular carcinoma.

Indian file pattern of growth of invasive lobular carcinoma.

Pleomorphic variant of invasive lobular carcinoma.

Cytoplasmic vacuolization with nuclear displacement in breast carcinoma due to lipid accumulation.

Signet ring carcinoma of the breast, this is regarded as a variant of lobular carcinoma. B, Alcian blue–PAS stain.

Signet ring carcinoma of the breast, this is regarded as a variant of lobular carcinoma. B, Alcian blue–PAS stain.

Immunocytochemical stain for estrogen receptors in invasive breast carcinoma. The strong nuclear positivity in tumor cells is shown against a negative cytoplasmic and stromal background.

Strong (3+) membrane immunoreactivity for HER2/neu in high-grade breast carcinoma.

Breast carcinoma metastatic to vertebra. The normal bone marrow has been flushed out by placing a thin slice of tissue under a strong jet of water.

Metastasis of mammary lobular carcinoma to lamina propria of large bowel mucosa. B, Keratin 7 immunostain.

Metastasis of mammary lobular carcinoma to lamina propria of large bowel mucosa. B, Keratin 7 immunostain.

Cluster of metastatic cells in sentinel lymph node highlighted with keratin stain.

Breast implant (left) surrounded by a thick fibrous wall that has undergone heavy calcification (right).

Striking vacuolization of breast carcinoma cells induced by chemotherapy. The appearance simulates that of histiocytes. The tumor cells shown in B are located within a blood vessel.

Striking vacuolization of breast carcinoma cells induced by chemotherapy. The appearance simulates that of histiocytes. The tumor cells shown in B are located within a blood vessel.

Benign mixed tumor of breast. A prominent myxochondroid stroma is interspersed among the glandular structures.

Adenoid cystic carcinoma of breast. The appearance is similar to that of its more common homolog in salivary glands.

Adenomyoepithelioma. In some areas there is a clear relationship

between the secretory and the myoepithelial component (similar to that seen in adenomyoepitheliosis), but in others the spindle myoepithelial cells become the exclusive neoplastic element.

Gross appearance of phylloides tumor. The tumor shown in A exhibits the typical appearance of the cut surface. The tumor illustrated in B has undergone extensive hemorrhagic infarct.

Gross appearance of phylloides tumor. The tumor shown in A exhibits the typical appearance of the cut surface. The tumor illustrated in B has undergone extensive hemorrhagic infarct.

Two views of low-grade phylloides tumor, showing cleft-like spaces and concentration of tumor cells beneath the epithelium.

Two views of low-grade phylloides tumor, showing cleft-like spaces and concentration of tumor cells beneath the epithelium.

Phylloides tumor with adipose tissue differentiation of the neoplastic stromal component.

Phylloides tumor with adipose tissue differentiation of the neoplastic stromal component.

Typical hemorrhagic gross appearance of angiosarcoma of breast.

Extremely well-differentiated angiosarcoma of breast.

Complex anastomosing vascular pattern in angiosarcoma of breast.

Benign hemangioendothelioma of breast in a child. The appearance is identical to that of the homologous tumor seen more commonly in skin or salivary gland.

Epithelioid (histiocytoid) hemangioma located within the breast substance.

Sarcoma of breast. The entrapped epithelial tissue lacks the features of a phylloides tumor.

MALT-type malignant lymphoma of breast. Some of the neoplastic lymphocytes infiltrate the glandular structures.

Granulocytic sarcoma of breast. It is easy to misdiagnose this lesion as a large cell lymphoma.

Gross appearance of so-called “hamartoma of breast.” There is a combination of cystic dilatation of ducts, fibrosis, and entrapment of adipose tissue. This lesion is more distinctive and impressive grossly than microscopically.

Glandular epithelium and fibrous stroma with distorted arrangement in hamartoma of breast.

So-called “myoid hamartoma of breast.”

Gross appearance of fibromatosis involving breast. The mass is solid and ill defined.

Pseudoangiomatous stromal hyperplasia. Thin channels lined by spindle cells are seen scattered within a hyalinized stroma.

Bizarre multinucleated cells in mammary stroma. This neoplastic change is analogous to that more often seen in the stroma of the upper aerodigestive tract and in the genital tract.

So-called “virginal hypertrophy of breast,”

showing proliferative changes in epithelium and stroma.

Juvenile papillomatosis (Swiss cheese disease). The gross appearance is that of clustered cystic formations.

Juvenile papillomatosis (Swiss cheese disease). Whole- mount view showing variously sized cystic formations, alternating with solid epithelial proliferations.

Epithelial proliferation surrounded by a hypocellular myxoid halo in gynecomastia.

Myofibroblastoma of male breast. The microscopic appearance is very reminiscent of solitary fibrous tumor.

Carcinoma of the male breast composed of well-

differentiated tumor cells with abundant granular cytoplasm having oncocytic features.

Grading of the immunohistochemical staining for HER2/neu overexpression