A molecular test can identify which types of tumors have an extremely low risk of leading to death from breast cancer, possibly helping to determine which tumors can be followed up and which can be left alone, according to a study published online June 29 in JAMA Oncology.
The study, led by Dr. Laura Esserman of the University of California, San Francisco (UCSF), investigated whether a 70-gene test called MammaPrint could identify slow-growing tumors and assess the risk of cancer recurrence up to 20 years after diagnosis. Esserman and colleagues collaborated with the Stockholm Breast Cancer Study Group to evaluate patients who had been tracked for years and were part of a randomized clinical trial of tamoxifen versus no systemic therapy.
The patient cohort was drawn from 652 lymph-node-negative patients with tumors 3 cm or smaller in diameter who had been part of the tamoxifen study from 1976 to 1990. All had their tumors surgically removed and were then randomized to two years of adjuvant tamoxifen (40 mg daily) versus no adjuvant treatment; of those included in the current study, 311 received tamoxifen and 339 did not.
As part of their treatment, tissue samples had been extracted from the women, and they were available for molecular analysis with MammaPrint. The researchers tested the removed tissue and classified women by the risk that their cancer would recur in the next 20 years; they then correlated these predictions with the actual clinical outcomes of the women, following them through 2012.
MammaPrint classified 42% of the patients as high risk and 58% as low risk; within the low-risk category, another 15% (n = 98) were categorized as ultralow risk. In this latter group, the women who received tamoxifen for at least two years had a 97% chance of survival from breast cancer at 20 years. This number stood at 94% for the patients with ultralow-risk tumors who did not receive tamoxifen.
How did this compare with the low-risk and high-risk patients? The high-risk women had a hazard ratio of 4.73 compared to the ultralow-risk women for breast cancer-specific death, while the low-risk women had a hazard ratio of 4.54.
The results suggest that the MammaPrint test can help physicians and patients determine treatment course and inform the choice of systemic therapy as well as local therapy, according to Esserman and colleagues.
"Women who have a tumor that is classified as ultralow risk by 70-gene signature can be reassured that their long-term outcome is expected to be excellent, with or without endocrine therapy," Esserman said in a statement released by UCSF. "Having a test that accurately identifies a population of women, who have very little risk to begin with, should be welcomed by patients and clinicians alike."
