Cancer of Unknown Primary
Cancer of unknown primary is defined as biopsy-proven malignancy for which the primary site of origin cannot be identified.
Pathology
These malignancies may include adenocarcinoma (60%), poorly differentiated carcinoma/poorly differentiated adenocarcinoma (29%), squamous cell carcinoma (5%), poorly differentiated malignant neoplasm (5%), and neuroendocrine carcinoma (1%).
Further identification may require specialized IHC staining, electron microscopy, and molecular/genetic analysis.Diagnostic Testing
In most cases, several studies are needed to facilitate a diagnosis, including comprehensive examination, urine/stool occult blood testing, and tumor marker testing in select patients (e.g., PSA in older men, #946;- hCG/AFP in younger men). CT of the chest, abdomen, and pelvis; PET CT; and symptom-oriented endoscopy may be useful in select patients.
TREATMENT
• Treatment for favorable subgroups of patients with cancer of unknown primary is tailored to the most likely primary site of origin. For instance, adenocarcinoma of unknown primary in women involving the axillary nodes is typically managed like stage II or III breast carcinoma. Papillary serous adenocarcinoma of unknown primary within the peritoneal cavity in women is typically managed as stage III ovarian carcinoma. The presence of blastic bone metastases and an elevated PSA in men is suggestive of stage IV prostate cancer and thus typically managed as such. Poorly differentiated midline carcinomas of unknown primary in men should be managed as extragonadal GCTs. Squamous cell carcinoma involving the cervical lymph nodes is typically managed as a locally advanced head and neck cancer, whereas squamous cell carcinoma involving isolated inguinal lymph nodes is typically managed with inguinal lymph node dissection with or without adjuvant radiation therapy.
• Poorly differentiated neuroendocrine carcinomas are typically managed with platinum-based chemotherapy regimens. A single, localized mass of unknown primary can be managed with definitive local treatment with either surgery or radiation, based on the location of the mass. Empiric combination chemotherapy regimen, such as carboplatin and paclitaxel, is typically considered in patients whose disease cannot be categorized into any of the favorable subgroups.