Treatment of advanced BRAF-mutated colorectal cancer: where we are and where we are going

Impact of early tumor shrinkage and depth of response in patients with BRAF V600E-mutant metastatic colorectal cancer

BACKGROUND

Early tumor shrinkage (ETS) and depth of response (DpR) are early indicators of survival in patients with metastatic colorectal cancer (mCRC) undergoing anti-epidermal growth factor receptor monoclonal antibody treatment. However, their relevance in v-raf murine sarcoma viral oncogene homolog B1 (BRAF) V600E mutant (MT) mCRC remains unclear. In this study, we evaluate the association between ETS/DpR and clinical outcomes in BRAF V600E MT mCRC.

PATIENTS AND METHODS

Patients with mCRC who were diagnosed with BRAF V600E MT and treated with first-line chemotherapy between June 2011 and March 2023 at a single cancer institute were enrolled. The association between ETS/DpR and clinical outcomes in patients with at least one target lesion was assessed. The cutoff value for ETS and DpR was set at 20% and 25%. Multivariate analysis of factors affecting progression-free survival (PFS) and overall survival (OS) was conducted.

RESULTS

In total, 54 patients with BRAF V600E MT mCRC exhibited at least one target lesion. Patients with ETS and DpR were 24 (44.4%) and 27 (50%), respectively. Moreover, median PFS and OS were 7.5 and 17.1 months, respectively. Patients with ETS exhibited longer PFS and tended toward longer OS than those without ETS. Similarly, patients with DpR exhibited longer PFS and OS than those without DpR. Multivariate analysis confirmed a significant association between DpR and longer PFS and OS.

CONCLUSION

ETS and DpR could serve as early surrogate markers of clinical outcomes in patients with BRAF V600E MT mCRC treated with first-line chemotherapy.

RAS/RAF mutations and microsatellite instability status in primary colorectal cancers according to HER2 amplification

HER2 amplification-associated molecular alterations and clinicopathologic features in colorectal cancers (CRCs) have not been well established. In this study, we assessed the prevalence of HER2 amplification and microsatellite instability (MSI) status of 992 patients with primary CRC. In addition, molecular alterations of HER2 amplified and unamplified CRCs were examined and compared by next-generation sequencing. HER2 amplifications were found in 41 (4.1%) of 992 primary CRCs. HER2 amplification was identified in 1.0% of the right colonic tumors, 5.1% of the left colonic tumors, and 4.8% of the rectal tumors. Approximately 95% of HER2 amplification was observed in the left colon and rectum. Seven (87.5%) of eight metastatic tumors showed HER2 amplification. Most clinicopathologic features were unrelated to HER2 amplification except tumor size and MSI status. All 41 HER2 amplified CRCs were microsatellite stable. In a molecular analysis of frequently identified somatic mutations in CRCs, HER2 amplified CRCs showed a lower rate of KRAS mutations (24.4%) but a higher rate of TP53 mutations (83%) than unamplified CRCs. No BRAF and NRAS mutations were identified in HER2 amplified CRCs. Our study suggests that HER2 amplified CRCs are mutually exclusive of MSI and harbor less frequent KRAS/NRAS/BRAF mutations but frequent T53 mutations.

Unanticipated pathological clearance in two cases of clinical T4b dMMR/MSI-h advanced colorectal cancer: the potential of immune checkpoint inhibitors despite positive positron-emission tomography results

BACKGROUND

The standard treatment for colorectal cancer consists of surgery and chemotherapy, which can be combined to improve outcomes. Immune checkpoint inhibitors (ICI) are a significant advancement in the standard treatment of metastatic, unresectable colorectal cancer with deficient mismatch repair (dMMR). However, limited data are available about the use of ICI in the neoadjuvant and conversion settings. Here, we present two cases treated with ICI.

CASE PRESENTATION

Case 1: A 75-year-old male with a large, borderline resectable rectal cancer diagnosed as cT4bN1bM0 who underwent neoadjuvant chemotherapy, followed by combination ICI consisting of ipilimumab and nivolumab. After four courses of ICI, the tumor significantly shrank, but positron emission tomography still showed a positive result and R0 resection was performed. Pathological analysis revealed no residual cancer cells. The patient has been monitored without adjuvant chemotherapy, and no recurrences have occurred after one year. Case 2: A 60-year-old male with locally advanced sigmoid colon cancer who received neoadjuvant treatment with pembrolizumab. The tumor partially shrank after three courses, and continued pembrolizumab monotherapy resulted in further tumor shrinkage which still showed positive positron emission tomography. Curative sigmoidectomy with partial resection of the ileum and bladder was performed, and the pathological outcome was pCR. There was no viable tumor in the specimen. The patient has been monitored without adjuvant chemotherapy for six months, and no recurrence has been observed.

CONCLUSIONS

The present study reports two cases, including a large, borderline resectable rectal cancer after failure of chemotherapy followed by combination treatment with nivolumab and ipilimumab and one case of sigmoid colon cancer after pembrolizumab treatment, which resulted in pathological complete response. However, it remains unknown whether ICI therapy can replace surgery or diminish the optimal extent of resection, or whether adjuvant chemotherapy is needed after surgery in the case of achieving pCR after ICI therapy. Overall, this case report suggests that ICI before colorectal surgery can be effective and potentially a 'watch-and-wait" strategy could be used for cases in which ICI is effective.

Activated MKK3/MYC crosstalk impairs dabrafenib response in BRAFV600E colorectal cancer leading to resistance

Colorectal cancer (CRC) patients with BRAF mutations develop resistance to BRAF inhibitors at a very early stage. Understanding the molecular mechanisms involved in BRAF inhibitor resistance is critical for the development of novel therapeutic opportunities for this subtype of CRC patients. CRC cells bearing BRAF mutations are mostly sensitive to the abrogation of Mitogen-Activated Protein Kinase Kinase 3 (MKK3), a specific activator of p38MAPKs signaling, suggesting that BRAF alterations might addict CRC cells to the MKK3/p38MAPK signaling. Interestingly, publicly available gene expression profiling data show significantly higher MKK3 transcript levels in CRC lines with acquired resistance to BRAF inhibitors. Herein, we investigated the roles of MKK3 in the response to BRAF targeting (dabrafenib) with COLO205 and HT29 BRAFV600E CRC lines and derived dabrafenib-resistant (DABR) sublines. Dabrafenib treatments reduce MKK3 activation by inducing autophagy in parental but not DABR cells. The MKK3 knockdown induces cell death in DABR cells, whereas ectopic MKK3 expression reduces dabrafenib sensitivity in parental cells. Mechanistically, activated MKK3 interacts and co-localizes with c-Myc oncoprotein (MYC), sustaining MYC protein stability and thus preventing the dabrafenib induced effects in CRC DABR cells both in vitro and in vivo. Overall, we identify a novel molecular mechanism beyond the dabrafenib resistance, shedding light on an uncovered vulnerability for the development of novel therapeutic opportunities in BRAFV600E CRC.