Colorectal cancer (CRC) is a common cancer in younger adults. In patients undergoing liver resection with RAS-altered CRCs, there is evidence suggesting younger patients have worse outcomes than older patients. To explain this pattern, differences in associations between RAS status and other cancer-related biomarkers in tumors from younger versus older patients with CRC were evaluated in a cohort of 925 patients with CRC, 277 (30.0%) of whom were ≤50 years old, and 454 (49.1%) who had RAS-altered tumors. For 3 biomarkers, RNF43, APC, and microsatellite instability (MSI), the association with RAS status was significantly modified by age after adjustment for multiple testing. Specifically, younger patients with RAS-altered tumors were more likely to be MSI-high, RNF43 mutated, and APC wild type. These differences might contribute to the observed pattern of diminished survival in younger versus older patients with CRC with RAS-mutated tumors undergoing liver metastasis resection.

With an estimated 1.88 million new cases and 0.92 million deaths in 2020, colorectal cancer accounts for nearly one-tenth of all new cancer and cancer-related deaths worldwide. Nearly half of the patients of colorectal cancer are diagnosed with metastatic or inoperable disease with a very dismal 5-year survival rate. Chemotherapy, targeted therapy, and immunotherapy have been used to treat metastatic disease, either alone or in combination. We present a case of recurrent metastatic colon carcinoma with KRAS exon 2 mutation and high microsatellite instability that was treated with a combination regimen of bevacizumab, capecitabine oral chemotherapy, and pembrolizumab immunotherapy. At nearly 5 years of treatment, the patient is alive with good performance status and improved quality of life owing to a favorable response to the molecular profiling-based treatment approach.

Pembrolizumab has been associated with a high tumor response rate among high microsatellite instability (MSI-H) cancer patients. The efficacy and safety of pembrolizumab in the treatment of MSI-H gastric cancer (GC) patients aged ≥ 85 years have not been reported. This study reports the case of an 89-year-old woman diagnosed with stage IIA MSI-H GC based on her chief complaint of abdominal pain. We considered surgery, but it was contraindicated due to the patient\'s age and cardiovascular comorbidity. Therefore, we administered pembrolizumab after receiving approval from the ethics committee, and no significant adverse events were noted. The tumor was markedly responsive to pembrolizumab, and the computed tomography and endoscopic findings revealed a complete response. This is the first report on the efficacy and safety of pembrolizumab in the treatment of GC in an \"oldest old\" patient with MSI-H.

On 21 January 2021, the European Commission amended the marketing authorisation granted for pembrolizumab to include the first-line treatment of microsatellite instability-high (MSI-H) or mismatch repair-deficient (dMMR) metastatic colorectal cancer (mCRC) in adults. The recommended dose of pembrolizumab was either 200 mg every 3 weeks or 400 mg every 6 weeks by intravenous infusion. Pembrolizumab was evaluated in a phase III, open-label, multicentre, randomised trial versus standard of care (SOC: FOLFOX6/FOLFIRI alone or in combination with bevacizumab/cetuximab) as first-line treatment of locally confirmed mismatch repair-deficient or microsatellite instability-high stage IV CRC. Subjects randomised to the SOC arm had the option to crossover and receive pembrolizumab once disease progressed. Both progression-free survival (PFS) and overall survival were primary endpoints. Pembrolizumab showed a statistically significant improvement in PFS compared with SOC, with a hazard ratio of 0.60 [95% confidence interval (CI): 0.45-0.80], P = 0.0002. Median PFS was 16.5 (95% CI: 5.4-32.4) versus 8.2 (95% CI: 6.1-10.2) months for the pembrolizumab versus SOC arms, respectively. The most frequent adverse events in patients receiving pembrolizumab were diarrhoea, fatigue, pruritus, nausea, increased aspartate aminotransferase, rash, arthralgia, and hypothyroidism. Having reviewed the data submitted, the European Medicines Agency\'s (EMA\'s) Committee for Medicinal Products for Human Use (CHMP) considered that the benefit-risk balance was positive. This is the first time the CHMP has issued an opinion for a target population defined by DNA repair deficiency biomarkers. The aim of this manuscript is to summarise the scientific review of the application leading to regulatory approval in the European Union.

OBJECTIVE: The efficacy of pembrolizumab for intrahepatic cholangiocellular carcinoma (IHCCC) is not widely reported.
METHODS: We began pembrolizumab treatment in a 69-year-old male with recurrent IHCCC at 18 months after his surgery because of the proven microsatellite instability (MSI)-high status. The patient had partial response, with an 82.5% reduction at the end of 18 courses. Immunostaining of the primary tumor revealed intra-tumoral infiltration of both PD-1+ and CD8+ T cells, and a low expression of PD-L1.
CONCLUSIONS: Intra-tumoral infiltration of both PD-1+ and CD8+ T cells may be a predictive factor of the efficacy of pembrolizumab. Expression of PD-L1 did not correlate with a therapeutic effect, but the tumor microenvironment of our patient\'s recurrent lesions may have been modified by conventional chemotherapy and CD8+ T cells.

Hepatocellular carcinoma (HCC) has limited systemic treatment options and a poor prognosis. The immune checkpoint inhibitor pembrolizumab was recently approved for the treatment of solid tumors with microsatellite instability (MSI). However, its clinical utility for the management of HCC remains to be clarified. Here, we present a case of unresectable HCC with MSI that showed an impressive response to pembrolizumab treatment. A 64-year-old man with chronic HCV infection was diagnosed with a large HCC. His severe liver dysfunction and poor performance status prevented any treatment option other than sorafenib. However, sorafenib failed after a few days due to the rapid progression of the tumor. Based on the finding of MSI in a biopsy specimen, immunotherapy using pembrolizumab was initiated. A dramatic improvement in his general condition and a reduction in tumor size were observed after the initiation of pembrolizumab treatment. Among a cohort of 50 consecutive patients with advanced HCC who were refractory to standard systemic therapy, MSI was found only in the present case. Immune checkpoint blockade therapy induced prominent anti-tumor effects in HCC with MSI. Screening for defects in DNA mismatch repair function may be warranted in HCC patients despite the low frequency of MSI.

To investigate patterns of programmed death protein-1 (PD-L1) expression in microsatellite instability (MSI)-high intestinal carcinomas and correlate them with pathologic and molecular features.
One hundred and fifteen MSI-high and 41 microsatellite stable carcinomas were included. Tumor sections were immunohistochemically labeled for PD-L1. The results were correlated with histologic subtypes, MSI, and BRAF status.
As expected, MSI status was associated with PD-L1 expression. Among 115 MSI-high tumors, PD-L1 expression was observed on tumor cells in 28 tumors and on tumor-associated inflammatory cells in 77 tumors. Medullary carcinoma demonstrated more frequent PD-L1 expression on tumor cells than mucinous and typical adenocarcinoma. PD-L1 expression was more frequent in medullary and typical adenocarcinoma than in mucinous adenocarcinoma based on combined positive scores. Tumors with more nucleotide shifts by PCR-based MSI testing were more likely to express PD-L1.
Expression of PD-L1 is different among different histologic subtypes of MSI-high intestinal carcinomas.