Peripheral Absolute Lymphocyte Count, Breast Cancer-Specific and Overall Mortality According to Race, Ethnicity, and Breast Cancer Subtypes

BACKGROUND: Low absolute lymphocyte count (ALC) is associated with breast cancer-specific mortality (BCM) and overall mortality (OM) in non-Hispanic (NH) White women with triple-negative breast cancer (TNBC). However, little is known about the relationship of ALC with BCM or OM in other breast cancer subtypes, racial or ethnic groups. Here, we investigated the association of ALC with BCM and OM by breast cancer subtype and evaluated for modification by race or ethnicity. METHODS: We used the Oncoshare database, linking data from electronic medical records of academic and community institutions to data from the California Cancer Registry, to identify women diagnosed with stage I-III breast cancer in 2000-2017 who had a post-diagnosis ALC within five years. We used logistic regression to identify factors associated with low ALC(<1 K/µL) and Cox models to evaluate the association of minimum ALC (minALC) post-diagnosis with BCM and OM. RESULTS: In 11,669 women, low ALC was associated with neutropenia, chemotherapy receipt, advanced stage, more comorbidities, and aggressive tumor features (all p≤0.001). Lower minALC was associated with higher OM(HR=0.96 per 1 K/µL increase, 95% CI 0.93-0.99), most strongly in TNBC(HR=0.73, 0.59-0.91). Race and ethnicity modified associations of minALC with BCM and OM (interaction p<0.001), more strongly in NH Black and Hispanic than NH White women. CONCLUSIONS: Low peripheral ALC was associated with higher OM in women with estrogen and/or progesterone receptor-positive, HER2-negative breast cancer or TNBC. IMPACT: Low ALC is more strongly associated with OM and BCM in women from minoritized racial and ethnic groups.