Colorectal Adenocarcinoma: Primary or Metastases? Utility of IHC Panel in Limited Resource Setting

Objectives: Primary colo-rectal adenocarcinoma is one of the common malignancies the world-over. Metastasis to colo-rectum is uncommon. We aim to study the clinical and histological features of a few cases of metastatic carcinoma from stomach, with an emphasis on immunohistochemistry to help us distinguish these tumours from colonic primary. Methods: Data from the laboratory information system was retrieved and biopsies/ resection specimen, taken from colon or rectum, with a diagnosis of metastatic adenocarcinoma from stomach with immunohistochemical studies supporting the same were included. Results: Previous history of carcinoma stomach is an essential part in diagnosing metastases to colo-rectum. Clues to diagnosis on histopathology include expanded lamina by bland looking/ signet ring cells with a relatively preserved colonic glandular mucosa. Useful panel of immunohistochemical stains include cytokeratin (CK) 7 and 20, epithelial membrane antigen (EMA) and CDX2. Conclusion: In a colonic biopsy with a relatively normal mucosa and signet ring cells in the lamina, the possibility of metastatic signet ring cell carcinoma from stomach should also be considered. Clinical history and imaging can be useful to correlate the findings. A small immunohistochemistry (IHC) panel with a minimum of 4 markers (CK7/20, CDX2 and EMA) serves as a valuable adjunct to confirm the same.