Primary pulmonary enteric adenocarcinoma in a young adult: a diagnostic and therapeutic challenge

Primary pulmonary enteric adenocarcinoma (PEAC) is a rare subtype of lung adenocarcinoma that resembles metastatic colorectal carcinoma in terms of morphology and immunophenotype. We describe a non-smoking female in her 30s who was referred for complaints of progressive low back pain, weight loss and fatigue. PET-CT revealed a 5.6 cm × 4.1 cm × 4.0 cm left lower-lobe mass in the lung, metabolically active left supraclavicular lymphadenopathy, a segment IV lesion of the liver and extensive bony metastases. A CT-guided biopsy revealed adenocarcinoma with mucin pools, and immunohistochemistry (IHC) showed diffuse positivity for CK7, CK20 and CDX2 and negativity for TTF-1, Napsin A and special AT-rich sequence-binding protein 2 (SATB2). These findings revealed the diagnosis of PEAC. She underwent 6 cycles of cisplatin and pemetrexed chemotherapy with tolerable toxicity and a partial metabolic response on follow-up PET-CT. This case underscores the importance of a multimodal approach to differentiate PEAC from metastatic colorectal cancer and facilitate appropriate treatment.