Phosphatidylinositol 3-kinases (PI3Ks) are lipid kinases involved in cellular growth and division. Somatic mutations in one of the PI3K catalytic subunit genes, PIK3CA, are frequently found in numerous malignancies, including colorectal cancer (CRC). Several PIK3CA inhibitors are approved for the treatment of breast cancer and lymphoma. Activating mutations in PIK3CA tend to occur in exons 9 and 20, with mutations in other exons 1, 4, and 7 being less common. Most test systems for PIK3CA mutation screening are designed to detect mutations in exons 9 and 20, leaving exons 1–7 overlooked. We have developed a multiplex AS-PCR to screen for PIK3CA mutations in exons 1, 4, 7, 9, and 20. Validation was performed on 515 CRC samples of patients from Siberia and the Far East of Russia. The assay sensitivity was 0.05–0.5% of mutant DNA, and the overall PIK3CA mutation frequency was 13.01%, with 9.32% of mutations in exon 9, 1.94% in exon 20, and 1.74% in exons 1–7. The assay designed is suitable for the analysis of activating PIK3CA mutations in formalin-fixed paraffin-embedded tissue samples. The present work is the first study characterizing the PIK3CA mutation frequency in CRC patients from the eastern part of Russia.

Compelling evidence demonstrates the importance of chromosome 8q24 as a locus of susceptibility to prostate cancer. In this work, the association of common 8q24 variants, rs6983267 and rs1447295, with a sporadic risk of prostate cancer was analyzed in the Russian population of Siberia. For this purpose, the above polymorphisms were genotyped in 393 cases and 384 control individuals. The A allele of rs1447295 was significantly associated with prostate cancer risk (OR[CI 95%] = 1.74 [1.26–2.4], p = 7.8 × 10⁻⁴). The common G-A haplotype of rs6983267-rs1447295 also showed association with prostate cancer risk in Russians (OR[CI 95%] = 2.03 [1.1–3.75], p = 0.02). A meta-analysis combining our data with previously published results was performed to better evaluate the association between the SNPs studied and prostate cancer risk; its results strongly supported the association for both loci (p < 10⁻⁶). Thus, our study has confirmed the association of chromosome 8q24 with a risk of prostate cancer.