Perianal Metastasis from Lung Adenocarcinoma Presenting as an Acute Abscess: A Case Report and review of the literature

Abstract Background: Lung cancer is one of the most common malignancies worldwide and frequently metastasizes to distant sites such as the liver, bones, and brain. Perianal involvement, however, is exceptionally rare. Case Presentation : A 76-year-old man with a 50-pack-year smoking history and a known pulmonary nodule presented with a one-month history of perianal pain and a three-month history of productive cough. Physical examination revealed a tender, erythematous perianal mass, leading to an initial diagnosis of perianal abscess. The patient underwent incision and drainage; intraoperatively, an indurated mass was noted, and histopathological examination unexpectedly revealed poorly differentiated adenocarcinoma with sarcomatoid differentiation. Subsequent bronchoscopic evaluation confirmed primary lung adenocarcinoma. The patient's clinical course was complicated by progressive pulmonary infection, ultimately resulting in fatal respiratory failure shortly after diagnosis. Conclusion: This case highlights an exceptionally rare pattern of metastatic lung cancer presenting as a benign anorectal condition. It underscores the importance of maintaining a high index of suspicion for metastatic disease in patients with atypical or refractory perianal lesions, particularly those with a history of malignancy or significant risk factors. Early histopathological evaluation is essential to avoid unnecessary surgical intervention and to facilitate timely initiation of systemic therapy.