Alpha-fetoprotein elevation in an asymptomatic young adult as a diagnostic clue to colorectal adenocarcinoma with enteroblastic differentiation.

Colorectal adenocarcinoma with enteroblastic differentiation (CAED) is a rare and aggressive histological subtype of colorectal adenocarcinoma characterized by the expression of enteroblastic markers, including alpha-fetoprotein (AFP), glypican-3, and spalt-like transcription factor 4 (SALL4). CAED typically affects older adults and is often diagnosed at an advanced stage. We report a rare case of AFP-producing CAED in a 29-year-old asymptomatic man whose markedly elevated serum AFP level served as a diagnostic clue. After elevated serum AFP was incidentally detected during a routine medical examination at a local clinic, markedly elevated serum AFP was confirmed at his initial visit to our hospital. Hepatocellular carcinoma and germ cell tumors were excluded by laboratory and imaging studies. Colonoscopy identified a transverse colon tumor, and the patient underwent curative resection. Histopathological examination demonstrated CAED with clear cytoplasm and positivity for AFP, SALL4, and glypican-3, confirming expression of all three enteroblastic markers. The pathological stage was pT3N2b, Stage IIIC. Serum AFP normalized after surgery, before the initiation of adjuvant chemotherapy, and the patient remains free of recurrence 12 months after surgery. This case highlights markedly elevated serum AFP as a potential diagnostic clue that may facilitate the early recognition of CAED, even in asymptomatic young adults.