Pembrolizumab and other immunotherapies have become central in treating metastatic colon cancer, particularly effective in patients with mismatch repair deficiencies. We report a case involving a man who initially underwent radical surgery for sigmoid colon cancer on April 27, 2011, followed by hepatic tumor resection on September 21, 2017. Post-surgery, he received eight cycles of adjuvant chemotherapy with the CAPEOX regimen and was regularly monitored through CT and MRI scans. On August 24, 2022, liver metastases were detected, and he was diagnosed with Lynch syndrome (LS) due to germline mutation in the MSH2 and EPCAM genes. He commenced treatment with 200mg of pembrolizumab intravenously every three weeks on September 2, 2022, and demonstrated a sustained response. However, after 17 cycles, he developed a treatment related adverse event (TRAE) of pancreatic endocrine dysfunction, leading to type 1 diabetes, managed with subcutaneous insulin injections. After 30 cycles of treatment, no evidence of disease was observed. This case underscores the significant clinical benefits of first-line pembrolizumab in managing hepatic metastasis in colonic carcinoma associated with LS, despite the occurrence of TRAEs. It raises critical questions regarding the optimal duration of immunotherapy following a complete or partial response and whether treatment should be discontinued upon the emergency of TRAEs. Continued research and forthcoming clinical trials with checkpoint inhibitors are expected to refine treatment protocols for LS-associated carcinoma.

Patients with Muir-Torre syndrome may have a systemic malignancy and a sebaceous neoplasm such as an adenoma, epithelioma, and/or carcinoma. The syndrome usually results from a germline mutation in one or more mismatch repair genes. Iatrogenic or acquired immunosuppression can promote the appearance of sebaceous tumors, either as an isolated event or as a feature of Muir-Torre syndrome and may unmask individuals genetically predisposed to the syndrome. Two iatrogenically immunosuppressed men with Muir-Torre syndrome features are described. Similar to these immunocompromised men, Muir-Torre syndrome-associated sebaceous neoplasms have occurred in solid organ transplant recipients, human immunodeficiency virus-infected individuals, and patients with chronic diseases who are treated with immunosuppressive agents. Muir-Torre syndrome-associated sebaceous neoplasms occur more frequently and earlier in kidney recipients, who are receiving more post-transplant immunosuppressive agents, than in liver recipients. The development of sebaceous neoplasms is decreased by replacing cyclosporine or tacrolimus with sirolimus or everolimus. Specific anti-cancer vaccines or checkpoint blockade immunotherapy may merit exploration for immune-interception of Muir-Torre syndrome-associated sebaceous neoplasms and syndrome-related visceral cancers. We suggest germline testing for genomic aberrations of mismatch repair genes should routinely be performed in all patients-both immunocompetent and immunosuppressed-who develop a Muir-Torre syndrome-associated sebaceous neoplasm.

BACKGROUND: Multiple primary malignancies are rare in cancer patients, and risk factors may include genetics, viral infection, smoking, radiation, and other environmental factors. Lynch syndrome (LS) is the most prevalent form of hereditary predisposition to double primary colorectal and endometrial cancer in females. LS, also known as hereditary nonpolyposis colorectal cancer (HNPCC), is a common autosomal dominant condition. Pathogenic germline variants in the DNA mismatch repair (MMR) genes, namely MLH1, MSH2, MSH6, and PMS2, and less frequently, deletions in the 3\' end of EPCAM cause LS. It manifested itself as loss of MMR nuclear tumor staining (MMR protein deficient, dMMR).
METHODS: This case study describes a double primary carcinoma in a 49-year-old female. In June 2022, the patient was diagnosed with highly to moderately differentiated endometrioid adenocarcinoma. The patient\'s mother died of esophageal cancer at age 50, and the father died of undefined reasons at age 70. Immunohistochemical stainings found ER (++), PR (++), P53 (+), MSH2 (-), MSH6 (+), MLH1 (+), and PMS2 (+). MMR gene sequencing was performed on endometrial tumor and peripheral blood samples from this patient. The patient carried two pathogenic somatic mutations in the endometrial tumor, MSH6 c.3261dupC (p.Phe1088LeufsTer5) and MSH2 c.445_448dup (p.Val150fs), in addition to a rare germline mutation MSH6 c.133G > C (p.Gly45Arg). Two years ago, the patient was diagnosed with moderately differentiated adenocarcinoma in the left-half colon. Immunohistochemical stainings found MSH2(-), MSH6(+), MLH1(+), and PMS2(+) (data not shown).
CONCLUSIONS: In the case of a patient with double primary EC and CRC, a careful evaluation of the IHC and the genetic data was presented. The patient carried rare compound heterozygous variants, a germline missense mutation, and a somatic frameshift mutation of MSH6, combined with a novel somatic null variant of MSH2. Our study broadened the variant spectrum of double primary cancer and provided insight into the molecular basis for abnormal MSH2 protein loss and double primary carcinoma.

A 47-year-old woman diagnosed with transverse colon cancer with liver, peritoneal, and lymph node metastases was admitted. Modified FOLFOX6(mFOLFOX6)regimen was given as a first line chemotherapy and was followed by pembrolizumab after 1 cycle of the mFOLFOX6, because microsatellite instability(MSI)test of the tumor showed high-frequency MSI. Because of the transverse colon obstruction after 2 cycles of pembrolizumab, she underwent right hemicolectomy. Histological examination of the resected specimen revealed no residual tumor cells in the primary tumor and reginal lymph nodes. Immunohistochemistry for mismatch repair proteins(IHC-MMR)showed loss of MSH2 and MSH6 expression. Genetic test identified a MSH2 pathogenic variant leading to the diagnosis of Lynch syndrome. The present case shows the importance of MSI test or IHC-MMR before the treatment of metastatic colorectal cancer.

Myxofibrosarcoma is a malignant fibroblastic neoplasm that commonly arises in the extremities, with mediastinum being a very rare location. The development of sarcomas is uncommon in patients with Lynch syndrome. We present a Lynch syndrome patient with synchronous cecal adenocarcinoma and mediastinal myxofibrosarcoma with both harboring the same loss-of-function MSH2 alteration (c.2634 + 1G > A splice region variant). Metastatic myxofibrosarcoma in the left chest wall developed 6 months after the initial diagnosis. The clinical presentation, imaging findings, histopathology, and molecular studies along with differential diagnoses are presented and discussed.

OBJECTIVE: Lynch syndrome (LS) is the secondary cause of hereditary ovarian cancer (OC). Germline mutations in the DNA-mismatch repair (MMR) genes cause tumorigenesis and a high immunogenicity. Recent studies showed a promising use of immunotherapy in MMR deficient (MMRd) tumors. This is a case report of a patient with LS-associated OC and a complete response to pembrolizumab.
METHODS: A 44-year-old patient was admitted to the hospital with lower abdominal pain. The patient\'s history showed LS with a germline mutation in the MSH2-gene. Initial diagnostics showed a pelvic tumor mass and a highly elevated cancer antigen 125. After debulking surgery, histopathological findings showed a high-grade serous OC with mutations in the MSH2 and MSH6 genes. Only 5 weeks after operation with no residual tumor mass, a quick and significant intraabdominal progression of the disease was diagnosed. Adjuvant therapy with carboplatin and paclitaxel in a weekly course did not lead to sustainable response. An anti-PD-L1 antibody therapy with pembrolizumab was initiated. After only two courses of therapy, the laboratory results and clinical status of the patient improved tremendously. Shortly after, a complete response was detected, and therapy is still ongoing. The patient remains tumor free for 21 months now.
CONCLUSIONS: The significance of germline compared to somatic mutations has not yet been sufficiently investigated. To our knowledge, this is the first case with complete response to checkpoint inhibition in OC associated with LS. Regarding LS-associated OC, immune checkpoint inhibition is an efficient therapy in tumors nonresponsive to standard therapy.

BACKGROUND: Epithelioid hemangioendothelioma (EHE) is a rare, low to moderate-grade malignancy, even less in pulmonary endovascular neoplasm. Patients with pulmonary EHE have no optimal treatment, resulting in poor prognoses.
METHODS: We reported a 42-year-old man with multiple mild metabolic uptakes in pulmonary endovascular filling defect with a maximum standardized uptake value of 4.5 by 18-fluorodeoxyglucose/fibroblast associated protein inhibitor-positron emission tomography/ computed tomography. Anticoagulant treatment was not effective with the diagnosis of acute pulmonary embolism.
METHODS: A primary endovascular EHE pulmonary endovascular epithelioid hemangioendothelioma was diagnosed by endovascular biopsy with positive stains for molecular CD31, CD34 and CAMTA1, and it had low proliferative capacity characterized by Ki-67 of 5%. The mutation gene MSH2 (p.Y656 in exon 12) (mutation abundance of 0.07%) from peripheral blood indicates the potential benefit of an immune checkpoint inhibitor, pembrolizumab.
RESULTS: The patient was treated with tri-weekly paclitaxel (175mg/m2) and carboplatin (AUC 5) chemotherapy regimen. He exerted a remarkable response after 5 cycles (21 days per cycle) and Pembrolizumab (200mg once monthly) as maintenance treatment.
CONCLUSIONS: This case highlights the diagnostic challenge of differentiating endovascular lesions and optimal therapy for pulmonary EHE. Importantly, it indicated that the mutation gene MSH2 (p.Y656) might influence the pathogenesis of EHE.

Lynch syndrome (LS) is a genetic disorder mainly caused by germline mutations in mismatched repair (MMR) genes (MSH2, MLH1, MSH6, and PMS2) or deletions of the epithelial cell adhesion molecule gene (EPCAM). A 43-year-old Chinese male patient underwent radical surgery and was pathologically confirmed to have stage IIIB colon adenocarcinoma. After four cycles of standard adjuvant chemotherapy, the tumor reoccurred in situ with intestinal obstruction. The patient received secondary colectomy. Immunohistochemistry analysis revealed a loss of MSH2 protein expression in the surgical specimen. Noticing that the patient\'s mother and grandfather all were diagnosed with LS-related cancers, we collected the patient\'s and his mother\'s peripheral blood for genetic testing, and the result showed a six-base deletion of MSH2. Thus, we concluded that our patient had LS. Subsequently, the patient accepted pembrolizumab as the first-line systemic therapy after liver metastases. He achieved clinical complete response (cCR) within 2 months and remained progression-free for more than 2 years. The case report showed that MSH2 mutation (c.489_494deTGGGTA) is a likely pathogenic mutation, and immunotherapy (pembrolizumab) is effective for this patient.

Several syndromic forms of digestive cancers are known to predispose to early-onset gastric tumors such as Hereditary Diffuse Gastric Cancer (HDGC) and Lynch Syndrome (LS). LSII is an extracolonic cancer syndrome characterized by a tumor spectrum including gastric cancer (GC). In the current work, our main aim was to identify the mutational spectrum underlying the genetic predisposition to diffuse gastric tumors occurring in a Tunisian family suspected of both HDGC and LS II syndromes. We selected the index case “JI-021”, which was a woman diagnosed with a Diffuse Gastric Carcinoma and fulfilling the international guidelines for both HDGC and LSII syndromes. For DNA repair, a custom panel targeting 87 candidate genes recovering the four DNA repair pathways was used. Structural bioinformatics analysis was conducted to predict the effect of the revealed variants on the functional properties of the proteins. DNA repair genes panel screening identified two variants: a rare MSH2 c.728G>A classified as a variant with uncertain significance (VUS) and a novel FANCD2 variant c.1879G>T. The structural prediction model of the MSH2 variant and electrostatic potential calculation showed for the first time that MSH2 c.728G>A is likely pathogenic and is involved in the MSH2-MLH1 complex stability. It appears to affect the MSH2-MLH1 complex as well as DNA-complex stability. The c.1879G>T FANCD2 variant was predicted to destabilize the protein structure. Our results showed that the MSH2 p.R243Q variant is likely pathogenic and is involved in the MSH2-MLH1 complex stability, and molecular modeling analysis highlights a putative impact on the binding with MLH1 by disrupting the electrostatic potential, suggesting the revision of its status from VUS to likely pathogenic. This variant seems to be a shared variant in the Mediterranean region. These findings emphasize the importance of testing DNA repair genes for patients diagnosed with diffuse GC with suspicion of LSII and colorectal cancer allowing better clinical surveillance for more personalized medicine.

Lynch syndrome (LS) is characterized by germline mutations in the DNA mismatch repair (MMR) genes. In colorectal cancer (CRC), germline mutations of DNA MMR genes commonly lead to microsatellite instability-high (MSI-H) subtype formation. Recent studies have demonstrated that CRC patients with MSI-H or mismatch repair-deficient (dMMR) status can benefit from anti-PD1 immunotherapy. However, almost 50% of CRC patients with MSI-H status do not respond to it. It is reported that heterogeneity of tumor and abnormal activation of cancer-related signaling pathways contribute to resistance to anti-PD1 therapy. To improve the clinical efficacy of such patients, the underlying mechanisms of resistance to anti-PD1 treatment must be explored. In this case, we describe an LS-associated CRC patient with MSI-H who suffered resistance to anti-PD1 therapy. Here, we attempted to elucidate the potential reasons, and thus appropriate strategies may be derived to overcome this clinical problem.