Women with luminal A breast cancer have better short-term survival but long-term survival curves don't level off

Women with luminal A breast cancer have lower mortality rates than those with other subtypes but continue to see a decrease in survival after 10 years of follow-up, according to a new study of molecular tumor subtypes.

Researchers from Kaiser Permanente Southern California used data from the health system's cancer registry to identify women who were diagnosed with invasive breast cancer from Jan. 1, 1988 to Dec. 31, 1995, and whose tumors were classified as luminal A, luminal B, basal-like, or HER2-enriched. To determine survival, patients were followed from the date of their surgery to death, disenrollment from the health plan or the study's end in 2008. The study results were published online Sept. 18 by Cancer Epidemiology, Biomarkers & Prevention.

A total of 934 women with a mean age of 59 years were included in the study. Most of the women (86%) were of non-Hispanic white ethnicity, and 32% were diagnosed with breast cancer before age 50. Most (66%) had the luminal A tumor subtype, while 22% had basal-like tumors, 7% had HER2-enriched tumors, and 5% had luminal B tumors.

Over the 21 years of the study, 223 women (23.9%) died of breast cancer. Women with luminal A tumors survived the longest, while those with HER2-enriched and luminal B tumors had significantly shorter survival times (P<0.0001). Women with basal-like tumors had intermediate survival but tended to die sooner than women with luminal A disease. Mortality risk was higher in women with HER2-enriched tumors (hazard ratio, 2.56; 95% CI, 1.53 to 4.29) and those with luminal B tumors (hazard ratio, 1.96; 95% CI, 1.08 to 3.54) compared with luminal A tumors.

In women with HER2-enriched and luminal B tumors, survival dropped steeply during the first three to four years of follow-up but then leveled off in subsequent years, while women with basal-like tumors had a sharper decline in the first two to two-and-a-half years and a more gradual decrease to approximately 13 years. Women with the luminal A subtype saw a steady decrease in survival persisting after 10 years of follow-up.

The authors acknowledged that some tumor subtypes may have been misclassified, that they did not have data on treatment for recurrent disease, and that their cohort was treated before certain targeted therapies were available, among other limitations. However, they concluded that in this cohort of women, molecular subtypes strongly predicted risk for death from breast cancer, with a higher overall mortality rate for HER2-enriched and luminal B tumors and a persistent long-term risk for the luminal A subtype.

“Despite its markedly higher survival probabilities in earlier years of follow-up, luminal A subtype was the only subtype that continued a steady drop in survival over the 20-year period with little leveling off in later years,” the authors wrote. They called for future studies to examine how the relationship between subtypes and survival varies by race and ethnicity and to determine factors to influence survival in women with luminal A disease.