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    Breast Cancer Biomarkers

    Home Breast Cancer Biomarkers
    Explore our Breast Cancer Biomarkers category for clear, practical guidance on the tests and molecular markers used to understand breast cancer biology, inherited risk, prognosis, treatment options, and disease monitoring. Topics include hormone receptor testing for estrogen receptor (ER) and progesterone receptor (PR), HER2 testing by IHC and FISH, HER2-low classification, and Ki-67 proliferation scoring. You’ll also find detailed guides to genomic and recurrence-risk tests such as Oncotype DX, MammaPrint, Prosigna PAM50, EndoPredict, Breast Cancer Index, and Mammostrat. The category also covers hereditary testing for BRCA1, BRCA2, PALB2, CHEK2, ATM, and multigene panels; actionable tumor markers such as ESR1, PIK3CA, and PD-L1; circulating tumor DNA and minimal residual disease (MRD); and blood tumor markers including CA 15-3 and CA 27.29. Subtype-focused biomarker panels for hormone receptor-positive and triple-negative breast cancer help connect individual test results with the larger clinical picture.
    Learn how the HER2 FISH test measures gene amplification, how HER2/CEP17 ratio and copy number define ISH groups, and what positive or negative results mean.

    HER2 FISH Test for Breast Cancer: Gene Amplification, HER2 Status, and...

    Learn how HER2 IHC scores 0, 1+, 2+, and 3+ are interpreted, what HER2-low and ultralow mean, when FISH is needed, and how results guide breast cancer therapy.

    HER2 IHC Test for Breast Cancer: Protein Expression Score, HER2-Low, and...

    Learn how HER2-low breast cancer is identified by IHC 1+ or IHC 2+/ISH-negative results, how scores are interpreted, and why HER2 expression can affect treatment.

    HER2-Low Breast Cancer Test: IHC Score, HER2 Expression, and Tumor Classification

    Understand ER, PR, ESR1, PIK3CA, HER2, and other tests in a hormone receptor-positive breast cancer biomarker panel, including what results can mean for treatment.

    Hormone Receptor-Positive Breast Cancer Biomarker Panel: ER, PR, ESR1, PIK3CA, and...

    Learn what a Ki-67 breast cancer score measures, how percentages relate to proliferation and tumor grade, which cutoffs are useful, and why results need clinical context.

    Ki-67 Breast Cancer Test: Proliferation Score, Tumor Grade, and Prognosis Meaning

    Learn how the MammaPrint 70-gene breast cancer test classifies genomic recurrence risk, what Low, High, and UltraLow results mean, and how it can inform chemotherapy decisions.

    MammaPrint Test: Breast Cancer Recurrence Risk and Genomic Risk Score

    Mammostrat was a five-protein breast cancer prognosis test that classified low, moderate, and high recurrence risk; learn how it worked, what old results mean, and why it is no longer used.

    Mammostrat Test: Breast Cancer Prognosis and Risk Classification

    Oncotype DX measures 21 tumor genes to produce a Breast Recurrence Score from 0 to 100; learn how node status, age, menopause, and pathology shape recurrence risk and chemotherapy decisions.

    Oncotype DX Breast Recurrence Score Test: Recurrence Risk, Genomic Score, and...

    PALB2 testing can reveal inherited DNA-repair variants linked to breast and family cancer risk; learn what positive, negative, and uncertain results mean and how they affect screening.

    PALB2 Test for Breast Cancer: Cancer Risk, DNA Repair, Variant Meaning,...

    PD-L1 testing in breast cancer uses tumor-tissue immunohistochemistry and CPS scoring; learn why CPS 10 matters in metastatic TNBC and why early-stage treatment is different.

    PD-L1 Test for Breast Cancer: Immunotherapy Marker, CPS Score, and Expression...

    PIK3CA testing detects PI3K-pathway mutations in breast cancer; learn how tissue and ctDNA results are interpreted and how positive findings can guide targeted therapy.

    PIK3CA Mutation Test for Breast Cancer: Mutation Status, PI3K Pathway, and...

    The progesterone receptor test measures PR nuclear staining in breast cancer; learn the 1% positive threshold, how PR is interpreted with ER, and what low or negative results mean.

    Progesterone Receptor (PR) Test: Breast Cancer Hormone Receptor Status, Positive Score,...

    Prosigna PAM50 measures breast tumor gene expression to report molecular subtype and a 0–100 Risk of Recurrence score; learn how nodal status and menopause shape interpretation.

    Prosigna PAM50 Test: Breast Cancer Subtype, Recurrence Risk, and Molecular Classification

    Understand TNBC biomarker testing for ER, PR, HER2, PD-L1 CPS, BRCA1/2, HER2-low status, and tumor profiling, including what results can mean for treatment.

    Triple-Negative Breast Cancer Biomarker Test: ER, PR, HER2, PD-L1, BRCA, and...

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