Breast Cancer Heterogeneity Examined by High-Sensitivity Quantification of PIK3CA, KRAS, HRAS, and BRAF Mutations in Normal Breast and Ductal Carcinomas

Abstract

Mutant cancer subpopulations have the potential to derail durable patient responses to molecularly targeted cancer therapeutics, yet the prevalence and size of such subpopulations are largely unexplored. We employed the sensitive and quantitative Allele-specific Competitive Blocker PCR approach to characterize mutant cancer subpopulations in ductal carcinomas (DCs), examining five specific hotspot point mutations (PIK3CA H1047R, KRAS G12D, KRAS G12V, HRAS G12D, and BRAF V600E). As an approach to aid interpretation of the DC results, the mutations were also quantified in normal breast tissue. Overall, the mutations were prevalent in normal breast and DCs, with 9/9 DCs having measureable levels of at least three of the five mutations. HRAS G12D was significantly increased in DCs as compared to normal breast. The most frequent point mutation reported in DC by DNA sequencing, PIK3CA H1047R, was detected in all normal breast tissue and DC samples and was present at remarkably high levels (mutant fractions of 1.1 × 10− 3 to 4.6 × 10− 2) in 4/10 normal breast samples. In normal breast tissue samples, PIK3CA mutation levels were positively correlated with age. However, the PIK3CA H1047R mutant fraction distributions for normal breast tissues and DCs were similar. The results suggest PIK3CA H1047R mutant cells have a selective advantage in breast, contribute to breast cancer susceptibility, and drive tumor progression during breast carcinogenesis, even when present as only a subpopulation of tumor cells.

The identification of pathogenic variants in BRCA1/2 negative, high risk, hereditary breast and/or ovarian cancer patients: High frequency of FANCM pathogenic variants

“…To date, pathogenic germline variants of HRAS have been associated with Costello syndrome (MIM #218040). Somatic HRAS‐ activating PVs are frequently found in salivary gland, urinary tract, upper aerodigestive tract and cervical cancer, but are rarely observed in breast cancer (< 1%) . Moreover, duplications of HRAS have only been found in tumors of male breast cancer patients carrying a pathogenic germline BRCA2 variant .…”

“…Somatic HRAS-activating PVs are frequently found in salivary gland, urinary tract, upper aerodigestive tract and cervical cancer, but are rarely observed in breast cancer (< 1%). 35,36 Moreover, duplications of HRAS have only been found in tumors of male breast cancer patients carrying a pathogenic germline BRCA2 variant. 37 It is unknown whether or not the observed HRAS duplication has a dosage effect or if aberrant HRAS expression influences tumor development at all.…”

miR-216b Post-Transcriptionally Downregulates Oncogene KRAS and Inhibits Cell Proliferation and Invasion in Clear Cell Renal Cell Carcinoma

“…Active GTP-bound KRAS associates with a wide variety of effectors, including Raf, PI3K, Ral-GDS, Rho GTPases and other molecules, to transmit downstream signals controlling distinct cellular events, including cell proliferation, survival, differentiation and invasion [17,23]. Interestingly, KRAS gene mutations are rare in breast cancer [24] and nasopharyngeal carcinoma [25], but its upregulation has been found in these tumors analyzed [26][27][28][29]. The same situation has been observed in renal cell carcinomas.…”

Integrating clinical, molecular, proteomic and histopathological data within the tissue context: tissunomics

“…Progression to cancer probably involves the accumulation of multiple field cancerisation driver mutations among synergistically acting groups of mutations . In this regard, molecular studies of peritumour areas in normal ducts of the breast or prostate may show a high number of genetic alterations and driver mutations . The clinical meaning of these molecular changes remains unknown, and further large studies are needed to establish their correlation with tumour relapse.…”