The implications of BRCA loss of heterozygosity (LOH) and deficient mismatch repair gene (dMMR) expression in the breast cancer of a patient with both inherited breast and ovarian cancer syndrome (BRCA2) and Lynch syndrome (MLH1)

A Japanese case of ovarian mucinous adenocarcinoma with germline double variants of MSH2 and BRCA2

Germline double heterozygosity (GDH) is rarely reported in cases of inherited cancer syndromes, and GDH of a mismatch repair gene and BRCA has never been reported in Japan. Nonetheless, the current report demonstrates a case of ovarian mucinous adenocarcinoma with initiated Lynch syndrome (LS)-related surveillance because of a known germline MSH2 variant. Six and a half years after oophorectomy, multiple tumors developed in the patient's lungs, bones, and lymph nodes, and histology results confirmed mucinous adenocarcinoma. Systemic chemotherapy including an anti-PD-L1 antibody was effective for >1 year, but brain metastases developed. Pathology of the brain tumors showed mucinous adenocarcinoma without expression of MSH2 and MSH6, while multi-gene panel testing demonstrated not only high microsatellite instability and a high tumor mutation burden, but also germline BRCA2 variants. Further, germline testing in relatives confirmed both variants were from the paternal line, from which many LS-related cancers develop, but not BRCA-related cancer.

Loss of heterozygosity results in rapid but variable genome homogenization across yeast genetic backgrounds

The dynamics and diversity of the appearance of genetic variants play an essential role in the evolution of the genome and the shaping of biodiversity. Recent population-wide genome sequencing surveys have highlighted the importance of loss of heterozygosity (LOH) events and have shown that they are a neglected part of the genetic diversity landscape. To assess the extent, variability, and spectrum, we explored the accumulation of LOH events in 169 heterozygous diploid Saccharomyces cerevisiae mutation accumulation lines across nine genetic backgrounds. In total, we detected a large set of 22,828 LOH events across distinct genetic backgrounds with a heterozygous level ranging from 0.1% to 1%. LOH events are very frequent with a rate consistently much higher than the mutation rate, showing their importance for genome evolution. We observed that the interstitial LOH (I-LOH) events, resulting in internal short LOH tracts, were much frequent (n = 19,660) than the terminal LOH (T-LOH) events, that is, tracts extending to the end of the chromosome (n = 3168). However, the spectrum, the rate, and the fraction of the genome under LOH vary across genetic backgrounds. Interestingly, we observed that the more the ancestors were heterozygous, the more they accumulated T-LOH events. In addition, frequent short I-LOH tracts are a signature of the lines derived from hybrids with low spore fertility. Finally, we found lines showing almost complete homozygotization during vegetative progression. Overall, our results highlight that the variable dynamics of the LOH accumulation across distinct genetic backgrounds might lead to rapid differential genome evolution during vegetative growth.

Double heterozygotes of BRCA1/BRCA2 and mismatch repair gene pathogenic variants: case series and clinical implications

BACKGROUND

Hereditary breast and ovarian cancer syndrome (HBOC) and Lynch syndrome (LS), the most common inherited cancer syndromes, are attributed to a single heterozygous pathogenic variant (PV) in BRCA1/2 or in a DNA MMR gene, respectively. Little is known about the phenotype in double heterozygotes who carry PVs in both genes.

METHODS

Carriers of double-PVs in any DNA MMR gene and BRCA1/2 attending one of three tertiary oncogenetic clinics between 1/2005 and 1/2020 were identified by database search, and their relevant data were retrieved and analyzed.

RESULTS

Eleven double carriers from four seemingly unrelated Ashkenazi Jewish families were evaluated. All carried an Ashkenazi Jewish founder BRCA PV, BRCA2 c.5946delT/c.6174delT (n = 10) or BRCA1 c.185delAG (n = 1). Four carried the MSH2 c.1906G > C founder PV, and 3, the MSH6 c.3984_3987dupGTCA founder PV; 3 patients had the MSH6 c.3956_3957dup PV. Eight double carriers (73%) had cancer: breast cancer (5 cases, 2 bilateral), melanoma (2 cases), urothelial cancer (2 cases), and colon, endometrial, prostate, cutaneous squamous cell cancer, glioblastoma, gastric stromal tumor, and lymphoma (1 case each). Six carriers had 1-2 tumors, one had 3 tumors, and one had 5 primary tumors. Age at diagnosis of the first tumor was 36-76 years. All carriers met NCCN BRCA1/2 testing criteria, and 3 met the revised Bethesda guidelines.

CONCLUSIONS

This case series, supported by the literature, suggests that the phenotype of double MSH2/6 and BRCA1/2 carriers is not associated with early disease onset or a more severe phenotype. The findings have implications for improved genetic testing guidelines and treatment strategies.

Gene Therapy as an Emerging Therapeutic Approach to Breast Cancer: New Developments and Challenges

Breast cancer is a heterogeneous disease, which is the consequence of several genetic and environmental factors. Also, it is one of the most common causes of cancer death and second leading cancer among women all around the world. Therefore, it is necessary to develop novel therapeutic approaches useful for the successful treatment of breast cancer. As conventional treatments had limited success, alternative approaches for the treatment of breast cancer have been applied in recent years. Hence, the molecular basis of breast cancer has provided the opportunity of using genetic materials for therapeutic uses. In this regard, gene therapy as one of the potentially efficient and beneficial treatments among various techniques became a popular treatment for different cancers, especially breast cancer. Accordingly, there are plenty of targets available for gene therapy of breast cancer. Gene therapy strategies have the potential to correct molecular defects that contributed to the cancer progression. These techniques should selectively target tumor cells without affecting normal cells. Moreover, data of clinical trials in gene therapy for breast cancer indicated that this approach has little toxicity compared to other therapeutic approaches. In this study, different aspects of breast neoplasm, gene therapy techniques, challenges, and recent developments will be mentioned.

GDF15 Repression Contributes to 5-Fluorouracil Resistance in Human Colon Cancer by Regulating Epithelial-Mesenchymal Transition and Apoptosis

Chemotherapy based on 5-fluorouracil (5-FU) is the standard approach for colon cancer treatment, and resistance to 5-FU is a significant obstacle in the clinical treatment of colon cancer. However, the mechanisms underlying 5-FU resistance in colon cancer cells remain largely unknown. This study aimed at determining whether 5-FU-resistant colon cancer cells undergo epithelial-mesenchymal transition (EMT) and apoptosis and the role of GDF15—a member of the transforming growth factor β/bone morphogenetic protein super family and a protein known to be involved in cancer progression—in the regulation of EMT and apoptosis of these cells, along with the underlying mechanisms. In vitro apoptosis detection assay, growth inhibition assay, transwell, and wound healing experiments revealed that 5-FU-resistant colon cancer cells possessed enhanced EMT and antiapoptotic ability. These cells also showed a stronger tendency to proliferate and metastasize in vivo. Quantitative reverse transcription-PCR and western blotting revealed that 5-FU-resistant colon cancer cells expressed lower levels of growth differentiation factor 15 (GDF15) than did 5-FU-sensitive colon cancer cells. Moreover, the transient GDF15 overexpression resensitized 5-FU-resistant colon cells to 5-FU. Collectively, these findings indicate the mechanism underlying the 5-FU resistance of colon cancer cells and provide new therapeutic targets for improving the prognosis of colon cancer patients.