Molecular subtypes of breast cancer in women ≤35 years and >35 years: Does age matter?

Background: Women diagnosed with breast cancer at young ages (≤35 years) have a substantially shorter overall survival durations. According to molecular pathological classification, triple negative and human epidermal growth factor receptor 2 (HER-2) positive breast cancer subgroups are related with poorer prognosis compared to luminal disease. Based on this rational, the primary objective was to evaluate the impact of age on determining molecular subgroups and whether the different outcomes of patients ≤35 years and >35 years of age are caused by the diversity of molecular subgroups. Methods: A total of 216 patients ≤35 years and randomly selected 212 patients of all breast cancer patients >35 years, presented to Ege University Department of Oncology were enrolled in the study. Molecular subtyping was based on estrogen, progesterone receptors (ER, PR), cerb-B2 and Ki-67 proliferation index assessed by immunohistochemistry. Luminal A disease was defined as ER (+), PR (+), cerb-B2 (-), Ki-67 ≤15. Patients with ER/PR (+), cerb-B2 (-)/(+), Ki-67 ≥15 were classified as Luminal B. If all three receptors were negative, it was accepted as triple negative disease and HER-2 positive disease was characterized by lack of hormone receptors and presence of cerb-B2. Results: Fifty-two percent in younger group were Luminal B and 19% were triple negative, which composed the largest proportion of the young group. Among the >35 years group the majority was Luminal B (39%) as similar in very young population, however, this was followed by Luminal A (31%) that has favorable prognostic features. Statistically, there was no significant difference in molecular subtypes between the two age groups. However, triple negative subtype and Ki-67 ≥15% which is associated with poorer prognosis, was numerically higher among ≤35 years of group. Conclusion: Young women diagnosed with breast cancer have poorer prognosis. However, in our study, there was no statistically significant difference in molecular subtypes between two diverse age groups. This could be explained by small size of the study population, but also could be an indication that age is an independent prognostic factor apart from other clinicopathologic features. Yet, since Luminal B and triple negatives were the largest subgroup in very young population, worse prognosis of the disease in this group may be explained by this diversion.