The MammaPrint test is a genomic assay that helps personalize treatment decisions for individuals with early-stage breast cancer. It evaluates a tumor’s biological characteristics, functioning as a prognostic tool to predict cancer recurrence. By analyzing a tumor’s genetic profile, MammaPrint guides patients and healthcare teams toward tailored treatment strategies.
Purpose of the MammaPrint Test
The MammaPrint test primarily predicts the long-term risk of breast cancer spreading to distant parts of the body within 10 years after diagnosis. This prognostic information helps determine if adjuvant chemotherapy after surgery would provide significant benefit. Chemotherapy carries considerable side effects, and the test can help patients avoid unnecessary exposure to intensive treatments. MammaPrint supports informed discussions between patients and physicians, optimizing treatment by identifying those who can safely forgo chemotherapy while ensuring others receive it.
How the Test Works and Who Is Eligible
The MammaPrint test analyzes the expression level of 70 specific genes found within the patient’s tumor tissue. This tissue sample is collected during a biopsy or surgery. RNA from these tumor cells is isolated and analyzed using microarray technology or next-generation sequencing to determine the gene expression profile. A proprietary algorithm then processes this profile to categorize the tumor’s risk.
Eligibility for the MammaPrint test includes patients with early-stage (Stage I or II) invasive breast cancer. Tumor size should be ≤ 5.0 cm. The test is validated for patients who are lymph-node negative (LN0) or have up to three positive lymph nodes (LN1-3). While most commonly used for estrogen receptor-positive (ER+) and HER2-negative breast cancers, MammaPrint can also be applied to ER-negative tumors, offering broader applicability.
Interpreting the Results
The MammaPrint test classifies a patient’s tumor as “Low Risk” or “High Risk” for distant recurrence. A “Low Risk” result indicates a low likelihood of the tumor spreading. For these patients, chemotherapy’s additional benefit is often minimal, and hormone therapy alone may be recommended. The chance of distant recurrence for low-risk patients is around 10% within 10 years without additional adjuvant treatment.
Conversely, a “High Risk” result signifies a higher likelihood of recurrence. In these cases, chemotherapy is typically recommended in addition to hormone therapy to reduce this risk. For high-risk patients, the chance of distant recurrence is approximately 29% within 10 years without additional adjuvant treatment. Some results may also include an “Ultra Low Risk” subgroup, indicating an even lower chance of recurrence with excellent long-term outcomes.
The MINDACT (Microarray In Node-negative Disease may Avoid ChemoTherapy) clinical trial supports MammaPrint’s utility. This study, involving nearly 6,700 patients, demonstrated MammaPrint could identify patients traditionally deemed at high clinical risk who, based on their genomic “Low Risk” profile, could safely forgo chemotherapy without compromising survival. The trial showed that omitting chemotherapy in these patients resulted in only a modest 2.6% difference in distant metastasis-free survival at 8 years compared to those who received chemotherapy.
Comparison with Other Genomic Tests
MammaPrint is one of several genomic tests guiding breast cancer treatment, alongside Oncotype DX. A primary difference is the number of genes analyzed: MammaPrint evaluates 70, while Oncotype DX assesses 21. This difference in gene panel size contributes to distinct biological insights provided by each test.
The way results are presented also differs. MammaPrint offers a binary “Low Risk” or “High Risk” classification, providing a clear indication for treatment decisions. In contrast, Oncotype DX provides a “Recurrence Score” ranging from 0 to 100, which is typically grouped into low, intermediate, and high-risk categories. MammaPrint also has broader applicability, validated for both estrogen receptor-positive (ER+) and estrogen receptor-negative (ER-) breast cancers, whereas Oncotype DX is primarily used for ER-positive, HER2-negative breast cancers. These distinctions mean that the tests may be suitable for different patient populations and offer varying levels of detail in their risk assessments.