PMC6590676_01
Microscopic appearance of the bone marrow (panels A and B) and of the affected intestinal wall after jejunal resection (panels C-I). Bone marrow immunohistochemistry for CD20 and annexin A1, showing strong and diffuse positivity, is depicted in panels A and B, respectively. Panel C: hematoxylin-eosin staining. Panels D-F: immunohistochemistry for CD3, CD56, and TIA-1, respectively. Panel G: negative immunohistochemistry for CD20 on affected intestinal tissue (no evidence of hairy cell leukemia cells). Panels H-I: immunohistochemistry for BRAF V600E on intestinal tissue (panoramic and magnified view). Note BRAF negativity on unaffected intestinal tissue.
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A hairy cell marrow infiltration was confirmed (Figure 1, Panels A-B), and the BRAF V600E fractional abundance remained persistently high (10.33%), indicating a lack of response. ANXA1- lymphoid elements, with a Ki-67 of 70%. CD56 and TIA-1 were also positive (Figure 1, Panels C-G). A diagnosis of MEITL was made. The expression of mutant BRAF was also confirmed by immunohistochemistry (Figure 1, Panels H-I).
Panel A: BRAF gene pyrosequencing on resected intestinal tissue, showing a T>A substitution in the affected tissue (upper diagram) and no mutation in unaffected margins (lower diagram). Panel B: analysis of the frameshift region 3 (FR3) of immunoglobulins on both marrow and intestinal samples. Proof of evidence of a reproducible 125 bp clone in both samples.
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Conversely, the mutation was absent on unaffected resection margins (Figure 2, Panel A), confirming a somatic - and not a germ-line - mutation. Therefore, it was possible to analyze only the frameshift region 3 (FR3) of immunoglobulins, which showed the presence of a reproducible 125 bp clone in both samples (Figure 2, Panel B).