Rare epithelial gastric cancers: a review of the current treatment knowledge

Gastric cancer (GC), one of the tumours with the highest mortality worldwide, is not a homogeneous disease, showing different features according to location, macroscopic aspect, histotype and molecular alterations. Adenocarcinoma is the most frequent epithelial GC (95%), the remaining 5% comprising rare epithelial tumours with their peculiarities, behaviour and incidence <6 cases/100,000/year. Due to the low number of cases, many aspects must be elucidated in this context. In this narrative review, we highlight the importance of a better understanding of rare GCs to personalize the cures in the light of the precision medicine concept. Our main aim is to translate the scarce evidence from the literature into daily clinical practice, never forgetting that all the clinicians dedicated to rare GCs should encourage such patients' enrolment in clinical trials and promote international collaborations. Hence, we focused on the treatment of the following rare GCs: rare gastric adenocarcinomas (hepatoid adenocarcinoma, medullary carcinoma with lymphoid stroma, Paneth cell carcinoma and Salivary Gland carcinoma); squamous cell carcinoma; adenosquamous carcinoma; neuroendocrine gastric neoplasms; gastroblastoma.