Constitutional mismatch repair deficiency (CMMRD) syndrome is characterized by biallelic mutations in a mismatch repair gene and is associated with development of childhood cancers and symptoms resembling neurofibromatosis type 1, like café-au-lait spots. We describe the extremely rare case of a 12-year-old male presenting with several light brown macular lesions on the skin, gastrointestinal diffuse large B-cell lymphoma, adenomatous polyposis throughout the gastrointestinal tract and an intra-abdominal invasive carcinoma derived from upper gastrointestinal system. All neoplasia, as well as normal tissues, showed loss of Msh6 expression with immunohistochemistry. Molecular studies showed pathogenic homozygous p.F1088Sfs*2 mutation in MSH6. Furthermore, signs consistent with immunodeficiency, namely decreased levels of IgG and IgA in the serum, nodular lymphoid hyperplasia and EBV-associated plasma cell proliferation with monotypic kappa light chain expression in the ileum, were also noted. Our case depicts the phenotypic diversity of CMMRD syndrome and emphasizes its association with immunodeficiency, raising awareness to a feature not widely recognized.

体质性错配修复缺陷 (CMMRD) 综合征的特征是错配修复基因的双等位基因突变，并且与儿童癌症的发展和类似于 1 型神经纤维瘤病的症状有关，如牛奶咖啡斑。我们描述了一名 12 岁男性的极其罕见的病例，该病例表现为皮肤上的几个浅棕色黄斑病变、胃肠道弥漫性大 B 细胞淋巴瘤、整个胃肠道的腺瘤性息肉病和源自上消化道的腹内浸润性癌。系统。所有瘤形成，以及正常组织，免疫组化显示 Msh6 表达缺失。分子研究显示MSH6中存在致病性纯合 p.F1088Sfs*2 突变. 此外，还注意到与免疫缺陷一致的体征，即血清中 IgG 和 IgA 水平降低、结节性淋巴样增生和 EBV 相关浆细胞增殖以及回肠中的单型 kappa 轻链表达。我们的案例描述了 CMMRD 综合征的表型多样性，并强调了它与免疫缺陷的关联，从而提高了对一个未被广泛认可的特征的认识。