Clinicopathological and molecular genetic characteristics of primary gastric follicular lymphoma.

Primary gastric follicular lymphomas (FLs) have been rarely reported, and little is known about their characteristics. In the present study, we report 5 cases of primary gastric FL and describe their clinicopathological and molecular genetic features. A total of 7 samples from 5 patients were investigated for clinicopathological characteristics and somatic mutations by the targeted sequencing of 50 lymphoma-related genes. Two cases were identified as slightly elevated submucosal tumors and 3 cases as polypoid tumors. Histologically, all cases were low-grade FLs. The immunoprofile was CD20+/CD10+/BCL2+ in 4 cases and CD20+/CD10+/BCL2- in 1 case. The immunostaining pattern for CD21 was similar to that of classic FL. BCL2 rearrangement was not identified in fluorescence in situ hybridization studies in any of the 5 cases. Next-generation sequencing analysis showed mutations in genes involved in epigenetic modifications (KMT2D, ARID1A, EP300, and CREBBP), NK-kB pathway (CARD11), and JAK-STAT pathway as found in classic FL. All cases presented with clinical I without the involvement of regional or systemic lymph nodes. Four patients were well, whereas 1 patient who received endoscopic mucosal resection of tumor without additional chemotherapy or radiotherapy experienced 3 relapses. In conclusion, primary gastric FL is characterized by a low-grade neoplasm with infrequent BCL2 rearrangement. After resection of the lesion, additional treatment such as radiation therapy or chemotherapy is required as there is a possibility of recurrence.