PIK3CA Mutation Analysis

PIK3CA is a gene that encodes a lipid kinase involved in multiple signaling pathways. These pathways influence cellular functions such as growth, death, and proliferation. PIK3CA mutations activate the PI3K-PTEN-AKT pathway, which is downstream from both the EGFR and the RAS-RAF-MAPK pathways. PIK3CA mutations may cause oncogenic transformation independent of RAS or RAF mutations.

PIK3CA mutations occur in about 15% to 30% of breast, endometrial, and colon cancers.^{1, 2} They occur less frequently in lung cancer and other types of cancer. Presence of PIK3CA mutations is associated with poor prognosis and lack of response to specific therapies in patients with breast, endometrial, or colon cancer. In lung cancers, PIK3CA mutations can identify prognostically relevant subgroups.

Breast Cancer

PIK3CA mutation predicts a lower pathologic complete response rate following anti-HER2 therapy in patients with HER2 amplification. PIK3CA mutations may also predict adverse outcome, independent of therapy, in certain breast cancer patient cohorts.

Colon Cancer

PIK3CA mutations predict a shorter disease-free and relapse-free survival. PIK3CA point mutations also forecast higher mortality rates in patients with wild-type KRAS tumors than in those with KRAS-mutated tumors.² PIK3CA mutations have been associated with resistance to anti-EGFR therapy (eg, cetuximab and panitumumab) in some studies^1,2 but not in others.^2-4 The reasons for the discrepancy are not clear.

Mutations in multiple genes are associated with colorectal cancer prognosis and response to therapy. So testing mutiple genes provides more complete information. The Quest Diagnostics Colorectal Cancer Mutation Panel (test code 18902) includes testing for mutations in KRAS, NRAS, BRAF, and PIK3CA. Thus, it includes testing for mutations in both EGFR downstream signaling pathways. Testing for mutations in these 4 genes can identify oncogenic mutations that result in bypass of EGFR signaling in 65% to 70% of colorectal cancer cases.³ Presence of 1 or more mutations predicts diminished response to anti-EGFR therapy.

Quest Diagnostics sequences exons 1, 9, and 20 of the PIK3CA gene. These exons harbor over 91% of all reported PIK3CA cancer-associated mutations.⁴ The most commonly encountered mutations, particularly those involving E542 and E545 in exon 9 and H1047 in exon 20, are associated with pathway activation, and their adverse effects are well supported by clinical data.⁵ The significance of less commonly observed PIK3CA mutations can sometimes be inferred based on structural and experimental studies.^5-7

DNA is extracted from formalin-fixed, paraffin-embedded tissue. Using PCR, the DNA in the entire coding region of exons 1, 9, and 20 is amplified. PCR products are subsequently purified and sequenced. We perform a forward and reverse dye-terminator Sanger sequencing method and gel capillary electrophoresis on an automated platform.

Our validation studies indicate this test is precise, accurate, and sensitive. The analytical sensitivity is 20% tumor cells in the background of normal cells. Testing is performed on the portion of the specimen where tumor is enriched.

Acceptable specimens include formalin-fixed, paraffin-embedded tissue blocks or slides with at least 5% tumor present, though at least 20% is preferred. Tissue that is not paraffin-embedded may be tested after review by the laboratory director. See the Quest Diagnostics test Directory for additional information: https://testdirectory.questdiagnostics.com

The patient report will include a list of mutations resulting in an amino acid change. If a rare mutation with an unknown clinical significance is detected, the report will include an interpretive comment based on a review of the available literature.

Results are typically reported within 7 days of specimen submission.