Answer: B - Epithelial-stromal polyp

Histologic sections demonstrate a spindle cell proliferation arranged in whorls that envelop and push adjacent crypts, which contain variable serrations. The cytoplasm is pale and eosinophilic with long tapering processes. The nuclei are ovoid and monomorphic, mitotic activity is inconspicuous. The serrated component is best classified as a sessile serrated polyp (sessile serrated lesion). Epithelial membrane antigen (EMA) shows patchy immunoreactivity, and molecular analysis shows a BRAF exon 15 mutation.

This subset of colorectal polyps, composed of serrated crypts that are enveloped and expanded by whorls of spindle cells, have been called benign fibroblastic polyps or, more commonly, perineuriomas. Most recently, however, it has been suggested that these lesions are best classified as epithelial-stromal polyps. When serrated crypts are present in these lesions, they have been found to be highly associated with other sessile serrated polyps and hyperplastic polyps. They often show a BRAF V600E mutation (95%) in the epithelial component and strong, patchy EMA staining of the spindle cell component (95%). The lack of BRAF mutation in the stromal component indicates the spindle cells are a reactive proliferation. In contrast, epithelial-stromal polyps with non-serrated crypts lack BRAF alterations and do not commonly show strong stromal staining by EMA.

Benign epithelial-stromal polyps with serrated epithelium are biologically similar to sessile serrated polyps and some authors have recommended for them to be classified as such to ensure appropriate clinical surveillance. The nature of epithelial-stromal polyps without serrated crypts is less clear, but their immunoprofile is not typical for perineuriomas.

Reference:

Hissong E, Yantiss R. Epithelial-Stromal Polyps of the Colon Are Not Perineuriomas, American Journal of Clinical Pathology, Volume 156, Issue 1, July 2021, Pages 109–116.