An Overview of the Pathology of Cancer of Unknown Primary

Morphologically, CUP can be classified as (1) well, moderately, or poorly differentiated adenocarcinoma; (2) squamous cell carcinoma; (3) poorly differentiated carcinoma; (4) carcinoma with neuroendocrine differentiation; and (5) undifferentiated cancer. Almost 50% of patients with diagnosed CUP have metastatic adenocarcinoma of well to moderate differentiation, 30% with undifferentiated or poorly differentiated carcinomas, 15% with squamous cell carcinomas, and the remaining 5% will have undifferentiated neoplasms.