Comprehensive characterisation of acinar cystic transformation of the pancreas: a systematic review

Aims: Acinar cystic transformation (ACT) of the pancreas is a rare pancreatic cystic lesion. Owing to its rarity, comprehensive histomolecular characterisation of this entity is still lacking. We aim to perform a systematic review on this controversial entity. Methods: We searched PubMed, SCOPUS and Embase through May 2023 to identify all studies on ACTs. Clinicopathological, immunohistochemical (IHC) and molecular data have been extracted and analysed. Results: Overall, there were 121 cases of ACTs in the literature. ACT had a female predominance (65.3% of patients), and a mean size of 4.8 cm. ACT was more often unifocal (71.9%) and multiloculate (61.2%). Histologically, the cysts were lined by an acinar epithelium, sometimes harbouring ductal-like areas (18.2%). In five cases (4.1%), an intralesional pancreatic intraepithelial neoplasia (PanIN) was reported. Preoperative diagnosis is challenging. After surgical resection, all patients were alive and disease free during follow-up except one patient who developed a second ACT after resection. By IHC, all lesions were positive for acinar markers; cytokeratin 7 and 8/18/19 were usually positive, and Ki-67 was invariably ≤3%. At the molecular level, three cases demonstrated genetic alterations: one showed multiple chromosomal gains, and other two harboured somatic mutations of KRAS and SMO genes (one mutation per case). Conclusions: Globally considered, our findings demonstrated that ACT is a benign entity, without the need of surgical resection with the exception of symptomatic lesions. The rare occurrence of intracystic PanINs and driver mutations suggest considering follow-up if a preoperative diagnosis of ACT can be made.