Chapter 095. Carcinoma of Unknown Primary (Part 2)

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Role of Imaging Studies Chest x-rays are always obtained in CUP workups but are often negative, especially with low-volume disease. CT scans of the chest, abdomen, and pelvis can be used to help find the primary, evaluate the extent of disease, and select the most favorable biopsy site. Older studies suggested that the primary tumor site is detected in 20–35% of patients who undergo a CT scan of the abdomen and pelvis, although by current definition these patients would not be considered as having CUP. ...

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Chapter 095. Carcinoma of Unknown Primary (Part 2) Role of Imaging Studies Chest x-rays are always obtained in CUP workups but are often negative, especially with low-volume disease. CT scans of the chest, abdomen, and pelvis can be used to help find the primary, evaluate the extent of disease, and select the most favorable biopsy site. Older studies suggested that the primary tumor site is detected in 20–35% of patients who undergo a CT scan of the abdomen and pelvis, although by current definition these patients would not be considered as having CUP. Older studies also suggest a latent primary tumor prevalence of 20%; with more sophisticated imaging, this prevalence is
Mammography should be performed in all women who present with metastatic adenocarcinoma, especially in those with adenocarcinoma and isolated axillary adenopathy. MRI of the breast is a recognized follow-up modality in patients with suspected occult primary breast carcinoma (following negative mammography and sonography findings). The results of these imaging modalities can influence surgical management; a negative breast MRI result predicts a low tumor yield at mastectomy. A conventional workup for a cervical CUP (neck lymphadenopathy with no known primary tumor) includes a CT scan or MRI and invasive studies, including indirect and direct laryngoscopy, bronchoscopy, and upper endoscopy. Ipsilateral (or bilateral) tonsillectomy (with histopathology) has been recommended for cervical CUP patients. [18]F-fluorodeoxyglucose (FDG) positron emission tomography (PET) scans are useful in this patient population and may help guide the biopsy; determine the extent of disease; facilitate the appropriate treatment, including planning radiation fields; and help with disease surveillance. Several studies have evaluated the utility of PET in patients with cervical CUP. These trials have included a small number of patients; primary tumors were identified in ~21–30%. The diagnostic contribution of PET to the evaluation of noncervical CUP is controversial. PET or PET-CT helps to detect primary tumor in 20–35% of patients. PET-CT can be helpful for patients who are candidates for surgical
intervention for solitary metastatic disease because the presence of disease outside the primary site will affect surgical consolidation planning. Invasive studies, including upper endoscopy, colonoscopy, and bronchoscopy, should be limited to symptomatic patients or those with laboratory or pathologic abnormalities suggesting that these techniques will result in a high tumor yield. Pathologic Diagnosis of CUP A detailed pathologic examination of the most accessible biopsied tissue specimen is mandatory in CUP cases. Pathologic evaluation typically consists of hematoxylin-and-eosin stains and immunohistochemical tests. Electron microscopy is rarely used currently, although it may be selectively useful when making treatment decisions. Light Microscopy Evaluation Adequate tissue obtained by fine-needle aspiration or core-needle biopsy should first be stained with hematoxylin and eosin and subjected to light microscopic examination. On light microscopy, 60% of CUPs are found to be adenocarcinoma, and 5% are squamous cell carcinoma. The remaining 30% of lesions are diagnosed as poorly differentiated adenocarcinoma, poorly differentiated carcinoma, or poorly differentiated neoplasm. A small percentage of
lesions are diagnosed as neuroendocrine cancers (2%), mixed tumors (adenosquamous, or sarcomatoid carcinomas), or undifferentiated neoplasm (Table 95-1). Table 95-1 Major Histologies in CUP Histology Proportion, % Well to moderately differentiated adenocarcinoma 60 Squamous cell cancer 5 Poorly differentiated adenocarcinoma, poorly 30 differentiated carcinoma Neuroendocrine 2 Undifferentiated malignancy 3