Rare case of adenocarcinoma with intestinal differentiation (PEAC) in the lung: Diagnostic challenges and treatment considerations

Adenocarcinoma with intestinal differentiation (PEAC) is a rare variant of lung adenocarcinoma, characterized by an enteric component and distinct immunohistochemical markers. This variant poses challenges in diagnosis and management due to its resemblance to primary colorectal adenocarcinoma and its unique clinical presentation. We present the case of a 76-year-old male with a one-month history of respiratory symptoms, initially managed as pneumonia. Subsequent evaluation revealed a left-sided pleural effusion, prompting further investigation. Histopathological analysis of pleural biopsy and immunohistochemistry confirmed PEAC, supported by positive staining for CK7 and CDX2. PET scan demonstrated malignancy in the left pleura and lung with likely metastasis to lymph nodes. The patient underwent anti-cancer treatment, but disease progression necessitated a change in therapy. PEAC often presents with nonspecific respiratory symptoms and is frequently misdiagnosed initially. Diagnosis relies on histopathological examination and immunohistochemical staining, emphasizing the importance of distinguishing it from primary colorectal adenocarcinoma and conventional lung adenocarcinoma. Treatment strategies for PEAC remain underexplored, and further research is warranted to establish optimal management approaches. • Recognition of PEAC as a variant of lung cancer • Differentiating PEAC from metastatic colon cancer • Importance of colonic serologic markers in PEAC • Choosing the correct therapy for PEAC