MammaPrint results place your breast cancer into one of two main categories: Low Risk or High Risk. The test analyzes the activity of 70 genes in your tumor tissue and produces a numerical index between -1.000 and +1.000. A positive score (0.001 to 1.000) means Low Risk, and a score at or below zero (-1.000 to 0) means High Risk. The purpose is to help you and your oncologist decide whether chemotherapy is likely to benefit you after surgery.
What the Index Score Means
Your report includes a numerical index that falls somewhere on a scale from -1.000 to +1.000. The dividing line sits at zero. Any score above zero is classified as Low Risk, meaning your tumor’s gene activity pattern is associated with a lower chance of the cancer spreading to distant parts of the body within the next 5 to 10 years. A score at or below zero is classified as High Risk, meaning the gene pattern suggests a higher probability of distant recurrence.
This is a binary result: Low Risk or High Risk. There is no “medium” category. However, where your score falls within each range still carries some meaning. A score of 0.90 reflects a more favorable gene expression pattern than a score of 0.05, even though both are technically Low Risk. Your oncologist may factor in how close your score sits to the zero threshold when discussing your treatment plan.
The Ultra-Low Risk Category
Within the Low Risk group, a subset of patients qualify for an additional classification called Ultra-Low Risk. This applies when your index score is 0.355 or higher. The distinction matters because ultra-low risk tumors behave extremely favorably over long time horizons. In one study tracking patients for 20 years, those with ultra-low risk scores who received hormone therapy had a 97% disease-specific survival rate. Even patients who received no systemic treatment at all had a 94% survival rate at 20 years.
In the original validation research, published in JAMA Oncology, no breast cancer deaths occurred among ultra-low risk patients treated with hormone therapy after 15 years of follow-up. If your report shows an ultra-low risk result, it suggests that your tumor biology is exceptionally favorable, and your oncologist will likely discuss whether you can safely forgo not only chemotherapy but potentially even some forms of hormone therapy.
How Risk Categories Translate to Survival Numbers
The practical difference between Low Risk and High Risk shows up in distant recurrence-free survival, which measures how many patients remain free of cancer spreading to other organs over time. In a clinical validation study from the Austrian Breast and Colorectal Cancer Study Group, Low Risk patients had a 94.0% distant recurrence-free survival rate at 5 years and 91.3% at 10 years. High Risk patients had rates of 91.6% at 5 years and 84.8% at 10 years.
That 6.5% gap at 10 years is the key number. It represents the additional risk of distant recurrence that High Risk patients face, and it’s one of the central pieces of evidence your oncologist uses to evaluate whether chemotherapy is worth the side effects. In the earlier prospective RASTER trial, Low Risk patients did even better: 97.0% remained free of distant recurrence at 5 years and 93.7% at 10 years.
What Your Result Means for Chemotherapy
The main clinical question MammaPrint answers is whether adding chemotherapy to hormone therapy will meaningfully reduce your risk of recurrence. The landmark MINDACT trial, published in the New England Journal of Medicine, enrolled nearly 6,700 patients and combined clinical risk assessment (based on tumor size, grade, lymph node involvement) with MammaPrint’s genomic risk score. The findings shaped how results are interpreted today.
If both your clinical risk and your genomic risk are low, chemotherapy is not recommended. If both are high, chemotherapy is generally advised. The most useful scenario is the “discordant” one: when your clinical features suggest high risk but MammaPrint returns a Low Risk result. The MINDACT trial showed that these patients could safely skip chemotherapy, with excellent outcomes. This is the group where MammaPrint changes the most treatment decisions, often sparing patients from unnecessary chemotherapy.
Patients whose clinical risk is low generally don’t benefit from chemotherapy regardless of what MammaPrint says. This is why current guidelines from the American Society of Clinical Oncology recommend ordering MammaPrint primarily when clinical risk is high, since that’s where the genomic result has the most power to change the plan.
BluePrint Subtyping on Your Report
Many MammaPrint reports also include results from BluePrint, an 80-gene molecular subtyping test that classifies your tumor into one of three biological categories: Luminal, HER2-type, or Basal-type. These subtypes reflect the underlying biology driving your cancer and can refine how your MammaPrint risk score is interpreted.
If your tumor is classified as Luminal by BluePrint, the MammaPrint score further divides it into Luminal A-type (Low Risk) or Luminal B-type (High Risk). Luminal A tumors tend to grow slowly and respond well to hormone therapy alone. Luminal B tumors are more aggressive and more likely to benefit from chemotherapy. Basal-type and HER2-type classifications indicate different biological drivers that influence treatment choices beyond what MammaPrint’s risk score alone conveys.
Updated NCCN guidelines now recognize this combined MammaPrint and BluePrint profile as a tool to guide specific chemotherapy decisions. Patients with High Risk Luminal B-type tumors (classified as “H2” in the reporting system) may be candidates for anthracycline-based chemotherapy regimens, while other high-risk patients might be treated with different approaches. MammaPrint remains the only genomic assay with FDA clearance for early-stage breast cancer and holds the highest level of evidence-based recommendation in NCCN guidelines for both node-negative and node-positive disease (up to 3 positive nodes).
Who the Test Is Validated For
MammaPrint is validated for patients with stage 1 or stage 2 invasive breast cancer, with tumors smaller than 5 centimeters, and with 3 or fewer positive lymph nodes. It works for both estrogen receptor-positive and estrogen receptor-negative tumors, which distinguishes it from some competing tests that are validated only for hormone receptor-positive cancers.
The test was originally developed and validated in patients with no lymph node involvement. Later European studies extended its validated use to patients with 1 to 3 positive nodes. If your cancer falls outside these parameters (larger tumors, more than 3 positive nodes, or later-stage disease), the test results may not be as reliable, and your oncologist would weigh them differently.
When Clinical and Genomic Risk Disagree
One of the most confusing situations is receiving a Low Risk MammaPrint result when your tumor’s clinical features, such as size, grade, or lymph node status, suggest you’re at higher risk. This discordance is actually common and is the exact scenario where genomic testing provides the most value. The MINDACT trial specifically demonstrated that patients in this discordant group (high clinical risk, low genomic risk) had favorable outcomes without chemotherapy.
The reverse discordance, low clinical risk but high genomic risk, is less clearly actionable. The MINDACT data showed that clinically low-risk patients generally did well regardless of genomic risk, which is why some guidelines suggest that genomic testing adds the most information for patients already identified as clinically high risk. If your result seems to conflict with what your oncologist initially expected based on your tumor characteristics, it doesn’t mean the test is wrong. It means your tumor’s gene activity tells a different story than its size or grade, and that genomic information is often more precise at predicting distant recurrence than traditional clinical features alone.
It’s also worth knowing that different genomic tests can disagree with each other. In one study of clinically high-risk tumors, MammaPrint and another genomic test gave discordant results in 44% of cases. This doesn’t invalidate your result, but it underscores that your oncologist interprets MammaPrint within the full context of your diagnosis rather than as a standalone verdict.