June 29, 2017. Dr. Laura Esserman, Chief, Section of Breast Care Surgery at UCSF and Director, UCSF Carol Franc Buck Breast Care Center, published a new study in JAMA Oncology demonstrating that the MammaPrint 70-gene recurrence-risk signature identifies a subgroup of breast cancers whose risk of recurrence was so low that endocrine therapy is not required.
The study was a genomic analysis of banked PPFE tumor samples collected during the Swedish STO-3 study. STO-3 was a randomized prospective study that enrolled 1,780 postmenopausal, lymph-node-negative patients with tumors less than or equal to 3 centimeters in diameter between 1976 and 1990.
All tumors were clinically detected and surgically removed, mostly by mastectomy and axillary dissection. Women in the study were randomized to two years of adjuvant tamoxifen (40 mg daily) versus no adjuvant treatment. In 1983, treated patients who were disease free after two years were reconsented to an additional 3 years of tamoxifen or no additional treatment. The participants in the study have been followed for more than 20 years.
Paraffin-embedded, formalin-fixed tumor samples from STO-3 were available for 808 women. 652 samples were of sufficient quality to run a MammaPrint risk assessment. Of these, 339 samples were from women who had received no adjuvant treatment. Based on prior studies, ultralow-risk tumors are identified as those having a risk scale value of greater than 0.355.
Of the 652 women who underwent a MammaPrint risk assessment. Twenty-year breast-specific survival in the treated (two-years) ultralow-risk group was 97%, as compared to 94% in the untreated group, a minimal difference. All the ultralow-risk tumors were luminal A on BluePrint typing. PAM50, Ki-67, and IHC-based analysis were not accurate in identifying ultralow-risk tumors. Although ultralow-risk tumors comprised 15% of the STO-3 study patients, up to 30% of screened-detected cancers in the United States may have ultralow risk.
Based on this, the authors assert that endocrine treatment in ultralow-risk patients is not necessary. The authors also feel that radiation treatment in this group may also be unnecessary and encourage further study to address this question.
Dr. Esserman’s study can be found at: http://jamanetwork.com/journals/jamaoncology/fullarticle/2634502