Background: The stromal microenvironment (SME) is integral to breast cancer (BC) biology, impacting metastatic proclivity and treatment response. Emerging data indicate that host factors may impact the SME, but the relationship between pre-diagnostic host factors and SME phenotype remains poorly characterized, particularly among women of African ancestry.
Methods: We conducted a case-only analysis involving 792 BC patients (17-84 years) from the Ghana Breast Health Study (GBHS). High-accuracy machine-learning algorithms were applied to standard H&E-stained images to characterize SME phenotypes (including percent tumor-associated connective tissue stroma, Ta-CTS (%), and tumor-associated stromal cellular density, Ta-SCD (%)). Associations between pre-diagnostic host factors and SME phenotypes were assessed in multivariable linear regression models.
Results: Decreasing Ta-CTS and increasing Ta-SCD were associated with aggressive, mostly high-grade tumors (p-value<0.001). Several pre-diagnostic host factors were associated with Ta-SCD independently of tumor characteristics. Compared with nulliparous women, parous women had higher levels of Ta-SCD [mean (standard deviation, SD) = 31.3% (7.6%) vs. 28.9% (7.1%); p-value=0.01]. Similarly, women with a positive family history of breast cancer had higher levels of Ta-SCD than those without family history [mean (SD) = 33.0% (7.5%)] vs. 30.9% (7.6%); p-value=0.03]. Conversely, increasing body size was associated with decreasing Ta-SCD [mean (SD) = 32.0% (7.4%), 31.3% (7.3%), and 29.0% (8.0%) for slight, average, and large body sizes, respectively, p-value=0.005].
Conclusions: Epidemiological risk factors were associated with varying degrees of stromal cellularity in tumors, independently of clinicopathological characteristics.
Impact: The findings raise the possibility that epidemiological risk factors may partly influence tumor biology via the SME.