Unexpected metachronous multiple primary cancers: pilonidal sinus‑related squamous cell carcinoma and incidentally detected gastric gastrointestinal stromal tumour.

This case report presents a 62‑year‑old male with chronic pilonidal disease that underwent malignant transformation into squamous cell carcinoma (SCC), followed 18 months later by incidental detection of a gastric gastrointestinal stromal tumour (GIST) during routine oncologic surveillance. Initial contrast‑enhanced CT revealed the gluteal SCC, which was surgically excised and treated with adjuvant radiotherapy. Subsequent CT scan indicates a well‑circumscribed mass in the submucosa of the stomach. MRI and endoscopic biopsy confirmed a submucosal gastric GIST, which was completely resected. No recurrence of either malignancy has been observed on follow‑up. This case underscores the pivotal role of multimodality imaging in diagnosis, staging, and longitudinal care.