MMR deficiency is frequent in colorectal carcinomas with diffuse SLFN11 immunostaining: clinicopathologic and molecular study of 31 cases identified among 3,300 tumors

Abstract

Schlafen 11 (SLFN11), a regulator of cell fate following DNA injury, sensitizes tumor cells to DNA-damaging agents. Patients with SLFN11-positive tumors may benefit from DNA-damaging chemotherapies. SLFN11 has been studied in different types of cancer including colorectal carcinomas. However, colorectal carcinomas with diffuse positivity (expression in ≥80% of tumor cells) have not been meticulously characterized. SLFN11 immunostaining of tumor microarrays (TMAs) with 3,300 primary CRCs identified 65 (~2.0%) tumors with focal staining (<10% of tumor nuclei positive), 83 (~2.5%) with patchy (≥10% and <80%) and 51 (~1.5%) with diffuse (≥80%) SLFN11 positivity. The latter was confirmed on full sections from donor blocks in 31 (~1%) cases, which were further studied including evaluation of additional immunohistochemical markers, genotyping with targeted DNA sequencing, and assessment of microsatellite instability. SLFN11-positive carcinomas were mostly (21/31, 68%) right-sided tumors with a female predominance (21/31, 68%) and median age of 67 years. Eighteen of 31 (58%) contained areas of mucinous differentiation. Deficiency of mismatch repair proteins was detected in 65% (20/31) of SLFN11-positive carcinomas. Moreover, MLH1 (n = 2), MSH2, MSH6, and PMS2 germline mutations were identified in 25% (5/20) of patients with mismatch repair deficient tumors. BRAF p.V600E mutation was found in 45% (9/20) of mismatch repair deficient, but only 1 of 11 proficient tumors. Colorectal carcinomas with diffuse SLFN11 positivity were often mismatch repair deficient tumors with their typical clinical, morphological, and molecular characteristics.

Keywords: DNA damaging agents; Lynch syndrome; SLFN11; colorectal cancer; mismatch repair proteins; mucinous carcinoma.

Figure 1

Clinicopathologic and molecular genetic characteristics of 31 CRCs with diffuse SLFN11 expression. Abbreviations (from the first to the last row left to right in consecutive order) are as follows: F, female; M, male; C, cecum; A, ascending, Hf, hepatic flexure; T, transverse; Sf, splenic flexure; D, descending; S, sigmoid; R/Sj, rectosigmoid junction; R, rectum; M diff, moderately differentiated; P diff, poorly differentiated; Muc, mucinous; S.ring, signet ring; 0, not present/negative/lack of expression; D, diffuse; Foc, focal; P, patchy; SC, scattered cells; Foc/0, indicates heterogeneity; Beta‐cat., β‐catenin; n., nuclear; S, substitution (missense mutation); fs, frameshift; *, STOP codon; superscript number, codon number; L, lost; #, intraglandular heterogeneity; Del, deletion; ger, germline; som, somatic; unk, unknown (germline versus somatic variant). Colors: blue – right colon; brown – left colon; yellow – not available; green – normal expression and WT; red – pathologic changes; orange and pink – possible pathologic changes. Dark and light gray mark female and male, respectively. Also, shades of gray are used to mark morphological differences. ddPCR assay: numbers indicate altered MSI markers.

Figure 2

Representative images. (A–C) Adenocarcinoma of the colonic hepatic flexure (case number 14) with mucinous differentiation (A, ×100) showing diffuse SLFN11 staining (B, ×100) and MSH6 loss (C, ×100) by immunohistochemistry; this tumor had mutations in MSH6 and KRAS genes. (D–F) BRAF V600E‐mutated carcinoma of the cecum (case number 4) (D, ×100) with SLFN11 positivity (E, ×100) and MLH1 loss (F, ×100).