Introduction: Mixed histology tumours are rarely found in the stomach. Of these, collision tumours are mainly composed of adenocarcinomas and sarcomas or lymphomas. This is the seventh case reported in the literature of an acinar cell carcinoma arising from an ectopic pancreas located in the stomach and the first described within a collision tumour.

Clinical case: We present the case of a 58-year-old female patient diagnosed with gastric cancer who, after undergoing a total gastrectomy, presented with a pathology report describing findings compatible with gastric collision tumour with components of tubular adenocarcinoma and acinar cell carcinoma of probable pancreatic ectopic aetiology.

Discussion: At the beginning of the 20th century, collision tumours were rarely described. Those located in the stomach are an infrequent pathology and are rarely diagnosed preoperatively. A collision tumour is composed of two independent neoplastic tissue with tumour areas separated in two different histological patterns and, in case of metastasis, this separation must also be clearly identified. There are different theories about its carcinogenesis and the debate regarding the ideal treatment is still ongoing.

Conclusion: This is the first report of a malignant gastric tumour with probable heterotopic pancreatic origin that collides with gastric adenocarcinoma.