CK7 (+), CK20 (-) favors which systems?

• A. GI Tract, Merkel Cell
• B. Skin, Adrenal Glands
• C. Lung, Breast, Thyroid, Salivary Gland, Uterus, Ovary
• D. Liver, Pancreas

Answer: (C)

CK7 positive and CK20 negative is a characteristic immunoprofile used to narrow the origin of carcinomas. CK7 is typically expressed in tumors from the lung, breast, thyroid, salivary glands, and the female genital tract (uterus and ovary), while CK20 is commonly seen in lower GI tract tumors (especially colorectal) and Merkel cell carcinoma. When a tumor shows CK7 positivity with CK20 negativity, it most strongly points to origins in the lung, breast, thyroid, salivary glands, uterus, or ovary rather than from the colon/rectum or Merkel cell. That’s why the option listing lung, breast, thyroid, salivary gland, uterus, and ovary fits this pattern best. The other choices reflect tissues more associated with CK20 expression or patterns that aren’t as consistent with CK7+/CK20−.