Katherine Geiersbach, M.D., explains how Mayo Clinic Laboratories' PIK3CA assay informs treatment for recurrent or progressing breast cancer. The assay identifies patients eligible for a certain second-line therapy when initial hormonal treatment has failed.

PIK3CA is a mutation present in 40% of breast cancers. In this test specific episode of the "Answers From the Lab" podcast, Katherine Geiersbach, M.D., explains how Mayo Clinic Laboratories' PIK3CA assay guides treatment decisions for certain types of breast cancer.

"The PIK3CA mutation test is used to determine eligibility for a kinase inhibitor treatment in a subset of patients with breast cancer," Dr. Geiersbach says. That subset is postmenopausal women or men who have hormone receptor-positive breast cancer that has progressed despite endocrine-based therapy. The kinase inhibitor, known as alpelisid, targets the PIK3CA mutation.

Mayo Clinic Laboratories offers PIK3CA testing using both breast tumor tissue and plasma. Dr. Geiersbach notes that most oncologists prefer tissue testing because the fraction of circulating tumor DNA in plasma may be low.

"It's important to have accurate and sensitive PIK3CA testing to select patients who would benefit from therapy and also to accurately detect the PIK3CA-negative patients who wouldn't benefit and might have toxicity from the therapy," Dr. Geiersbach says.

Listen to learn more about Mayo Clinic Laboratories' PIK3CA testing.

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Testing

PIK3B | Cell-Free DNA PIK3CA Test, Blood

PIK3T | PIK3CA Mutation Analysis, Tumor

Useful information

PIK3B | Cell-Free DNA PIK3CA Test, Blood

Identification of hormone receptor positive and human epidermal growth factor receptor 2 negative (HR+/HER2-) advanced breast cancer tumors that may be eligible for treatment with targeted kinase inhibitor therapy (eg, alpelisib).

PIK3T | PIK3CA Mutation Analysis, Tumor

Identification of hormone receptor positive and human epidermal growth factor receptor 2 negative (HR+/HER2-) advanced breast cancer tumors that may be eligible for treatment with targeted kinase inhibitor therapy (eg, alpelisib).

Specimen requirements

PIK3B | Cell-Free DNA PIK3CA Test, Blood

• Specimen Type: Whole Blood
  • Samples should be transported at ambient temperature or refrigerated (4 degrees C)
  • Samples are viable for 7 days in the Streck Black/Tan Top Tube Kit
• Supplies: Streck Black/Tan Top Tube Kit (T715)
• Specimen Volume: Two, 10-mL Streck cell-free DNA (cfDNA) blood collection tubes

Additional Information:

• Only blood collected in Streck cfDNA tubes will be accepted for analysis.
• Whole blood will be processed to produce platelet-poor plasma before cfDNA isolation.

PIK3T | PIK3CA Mutation Analysis, Tumor

• Specimen Type: Varies

NECESSARY INFORMATION:

A pathology report (final or preliminary), at minimum containing the following information, must accompany specimen for testing to be performed:

• Patient name
• Block number-must be on all blocks, slides, and paperwork (can be handwritten on the paperwork)
• Tissue collection date
• Source of the tissue

SPECIMEN REQUIRED

This assay requires at least 20% tumor nuclei.

The amount of tissue needed is dependent on a variety of preanalytical factors (eg, cellularity, ischemic time, fixation). The FFPE input required is equivalent to a 4 to 5 micron slide thickness with a total tumor surface area of 100 mm(2). This can be created by combining material from multiple slides from one tissue block.

Preferred:

• Specimen Type: Tissue block
• Collection Instructions: Submit a formalin-fixed, paraffin-embedded tissue block.

Acceptable:

• Specimen Type: Tissue slide
• Slides: 1 stained and 10 unstained
• Collection Instructions: Submit 1 slide stained with hematoxylin and eosin and 10 unstained, nonbaked slides with 5-micron thick sections of the tumor tissue.
• SPECIMEN MINIMUM VOLUME: See Specimen Required

Performance information

PIK3B | Cell-Free DNA PIK3CA Test, Blood

Analytic time: 5 to 10 days

Days performed: Monday through Friday

PIK3T | PIK3CA Mutation Analysis, Tumor

Analytic time: 8 to 12 days

Days performed: Monday through Friday

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