Pulmonary Metastasis of Anal Squamous Cell Carcinoma Nine Years Following Treatment

Squamous cell carcinoma of the anus (SCCA), the predominant histologic subtype of anal cancer, is associated with human papillomavirus (HPV) infection in over 90% of cases. The risk of SCCA is markedly elevated in individuals with HIV, particularly those experiencing advanced or prolonged immunosuppression. Most local recurrences occur within three to five years of initial treatment, while distant metastases develop in 10-20% of patients following curative therapy. At diagnosis, distant metastases are identified in only 5-8% of cases. Prognosis varies significantly by stage, with a five-year overall survival of approximately 78% in localized disease and 19% in cases with distant metastasis. We report a rare case of delayed pulmonary metastasis of SCCA in a 51-year-old man with HIV and a history of inconsistent adherence to highly active antiretroviral therapy (HAART). The patient had undergone definitive chemoradiation for anal squamous cell carcinoma nine years earlier, with no evidence of recurrence on routine surveillance. He presented to the emergency department with a four-day history of night sweats, chills, chest pain, abdominal discomfort, hematochezia, and unintentional weight loss. Computed tomography (CT) angiography revealed a 2.7 cm spiculated nodule in the left lower lobe of the lung, initially raising concern for a primary pulmonary malignancy. However, CT-guided biopsy demonstrated squamous cell carcinoma positive for P40 and P16, consistent with HPV-associated disease originating from the anorectal region. Colonoscopy revealed no signs of local recurrence. This case highlights an exceptionally prolonged interval between curative treatment and metastasis of SCCA and raises important questions about the role of intermittent HAART adherence in long-term oncologic outcomes. It also underscores the need for clinicians to maintain a high index of suspicion for metastatic spread or recurrence of prior cancers in immunocompromised patients, even in the absence of local symptoms. Additional research is necessary to improve long-term surveillance strategies and mitigate recurrence risk in this vulnerable population.