Patients with breast cancer who are younger than 40 years are likely to have unfavorable subtypes, higher stage, and lower overall survival and disease-free survival (DFS) as compared to their older counterparts, according to researchers at the Roswell Park Cancer Institute in Buffalo, NY. They presented their findings on Friday, December 8, during the San Antonio Breast Cancer Symposium

Young and colleagues noted the incidence of breast cancer in young women in the U.S. has been relatively low and stable, but the absolute number of young women with breast cancer is increasing because of the growing population. Some epidemiological studies have shown that breast cancer diagnosed before age 40 have significantly worse overall 5-year survival, they added. Further, DFS is also inferior in younger women, and the younger patient tends to have more aggressive cancer.

The group used data from The Cancer Genome Atlas ([TCGA], n = 1,095) and the Molecular Taxonomy of Breast Cancer International Consortium ([METABRIC], n = 1,894) to analyze young (< 40 years old) and non-young (> 40 years old) cohorts.

Overall, few young patients were found in either dataset (98 in TCGA and 116 in METABRIC). In the young cohort, A total of 69.5% (n = 64) and 37.9% (n = 44) in the young cohort were estrogen receptor positive (ER+) whereas 77.9% (n = 742) and 79.5% (n = 1415) in the non-young cohort were ER+ for the TCGA and METRABRIC datasets, respectively.

Similar results were found for TCGA and METABRIC dataset (respectively) for progesterone receptor-positive (PR+) tumors: 60.8% (n = 56) and 31.9% (n = 37) were PR+ in the young cohort compared to 68.4% (n = 641) and 54.4% (n = 972) in the non-young cohort. Human epidermal growth factor receptor 2-positive (HER2+) cancers were noted in 22.2% (n = 12) and 25% (n = 29) in the young cohort and in 22.6% (n = 152) and 11.6% (n = 207) in the non-young cohort.

The researchers then developed a pipeline to calculate PAM50 gene signatures and found there were fewer patients with luminal A and B subtype markers in the young cohort (41.6% [n = 42] and 17.8% [n = 18] compared to 49.7% [n = 377] and 22.9% [n = 174] in the non-young cohort in the TCGA dataset and 17.2% [n = 20] and 9.5% [n = 11] in the young group compared to 36.9% [n = 659] and 25.2% [n = 450] in the non-young group from the METABRIC dataset). More basal-like subtypes were found in the young group.

The young group had about half the number of patients with stage I disease compared to the non-young group in both datasets but about the same percentage of stage II young patients in both datasets. The numbers reversed when analyzing stage III disease: the incidence is increased in the young group at 31.2% (n = 30) and 16.1% (n = 14) compared to 22.4% (n = 219) and 7.7% (n = 101) in the non-young cohort in TCGA and METABRIC, respectively.

Young patients had a lower median DFS than non-young patients (data not available versus 214.7 months, p = 0.027); however, no statistical significance existed in median survival. Young patients had a lower median disease-specific survival than non-young patients of 221.1 months versus 282.6 months (p = 0.00123) in METABRIC.

The researchers said that more analysis with genomics is still needed.