Collision tumors are rare cases with two different tumor entities growing synchronously. While adenocarcinoma of the pancreas is the most common pancreatic tumor with an incidence of 10 per 100.000, retroperitoneal liposarcoma remains very rare. This is the first report of a collision tumor between these two tumor entities.Demographic details: The tumor was diagnosed in a 64 male Caucasian patient. Besides atrial fibrillation, arterial hypertension and a hypothyroidism there is no relevant medical history especially no history of cancer. Clinical details: During a routine check-up an unclassified tumor of the pancreatic tail was diagnosed. The lab showed no pathologies. Tumor markers were negative for carbohydrate antigen 19-9 and 72-4 (CA 19-9, CA 72-4) and carcinoembryonic antigen (CEA). Alpha-fetoprotein (AFP) and neuron specific enolase (NSE) were both elevated (AFP 97kU/l, (< 5,8kU/l) and NSE 30,0 μg/l (16,4 μg/l)). A computed tomography-guided core needle biopsy was performed which revealed a low-grade liposarcoma (G1). A CT scan showed no metastases. A surgical resection was recommended by the interdisciplinary tumor board.A systematic left sided retroperitoneal compartment resection including en-bloc-left sided pancreatectomy, splenectomy, nephrectomy, hemicolectomy, adrenalectomy, partial gastrectomy and partial resection of the diaphragm was performed. Pathology revealed a collision tumor consisting of pancreatic adenocarcinoma that was classified pT3, pN2 (11/33 ece+) L1 V0 Pn0, R0; G2 [UICC Stage III] and a liposarcoma pT2, pN0 (0/33) L0 V0 Pn0, G1 [UICC Stage Ib]. The postoperative tumor board recommended an adjuvant chemotherapy with gemcitabine and capecitabine for the locally advanced pancreatic adenocarcinoma.At the latest follow-up (1 year after surgery) the patient was in good clinical condition and without evidence of tumor recurrence.Collision tumors are rare and difficult to diagnose. This is the first description of a collision tumor composed of pancreatic adenocarcinoma and retroperitoneal liposarcoma. The reported case demonstrates that inconsistent diagnostic results (e.g. imaging and pathology) should raise suspicion concerning the diagnosis. Awareness of these rare cases might protect us from underdiagnosing patients and therefore leading to better patient care. There is evolving evidence that will lead to more personalized treatment options for somatic BRCA mutated pancreatic cancer.
