A rare solid tumor frequently misdiagnosed as lymphoma: primary colonic Epstein-Barr virus-positive inflammatory follicular dendritic cell sarcoma.

BACKGROUND

Primary colonic Epstein-Barr virus-positive inflammatory follicular dendritic cell sarcoma (EBV+ iFDCS) is a rare, poorly characterized neoplasm. This study aims to delineate its clinicopathological features and thereby facilitate accurate diagnosis.

METHODS

This study retrospectively analyzed 14 cases of primary colonic EBV+iFDCS and conducted a systematic review of 18 additional cases from the literature.

RESULTS

The median age was 51 years (range, 35-68 years), with 10 females and 4 males. All cases were confined to the colon, with the transverse colon as the most common site (50%, 7/14), followed by the descending colon (28.6%, 4/14), sigmoid colon (14.3%, 2/14), and ascending colon (7.1%, 1/14). The vast majority of cases (85.7%, 12/14) were asymptomatic and were incidentally detected during routine physical examinations. Endoscopically, the tumors presented as either pedunculated polyps (9 cases) or sessile polypoid lesions (5 cases) with surface congestion. Their histology was characterized by mucosal erosion, prominent superficial perpendicular vessels, and secondary lymphoid follicular (SLF)hyperplasia. Neoplastic spindle cells were arranged in scattered and fascicular patterns within a background of plasma cells and small lymphocytes. Morphological subtypes comprised classic/lymphoma-like mixed type (64.3%, 9/14) and lymphoma-like type (35.7%, 5/14). Tumor cells expressed multiple FDC markers (CD21, CD23, CD35), co-expressed SMA (100%, 13/13) and CD56 (100%, 12/12), while SSTR2 was typically negative or only weakly expressed. The microenvironment was characterized by a B-cell predominance. EBV-encoded RNA was detected in perivascular and interfollicular tumor cells, with positivity also in germinal center FDCs. Clonality assays were negative in all but two cases (one case each with TCR rearrangement and IG rearrangement). All patients were underwent endoscopic submucosal resection, with no recurrence or major complications.

CONCLUSION

Primary colonic EBV+iFDCS is a distinct, low-grade malignant neoplasm that typically presents as polyp or polypoid lesion. Its hallmark histologic features include a characteristic arrangement of vessels and SLFs in a prominent lymphocytic background. The tumor exhibits a dual immunophenotype, expressing markers of both FDCs and follicular reticular cells. Because the disease follows an indolent clinical course with a favorable prognosis, accurate diagnosis is essential to avoid overtreatment.