Treatment differences between urban and rural women with hormone receptor-positive early-stage breast cancer based on 21-gene assay recurrence score result.

Abstract

Breast cancer is the most common invasive cancer in women in the United States, and the second leading cause of cancer death.1 Differences in breast cancer mortality have been linked to socioeconomic and population differences, but the etiologic relationship among these factors remains unclear.2 Although some studies have found that rural populations have an increased overall breast cancer-associated mortality,2 others have suggested decreased mortality3 or no difference after adjusting for age, sex, or race.4,5 Proposed factors that possibly contribute to increased mortality in rural patients include presentation with later stage dis-ease,4,6,7 less access to mammographic screening,8,9 lower socioeconomic status,10 and less access of because of geographic location to newer more effective therapies and technologies.11,12 Individual risk factors13,14 such as body mass index (BMI),15,16 parity,13 or differences in exogenous hormone use17 may also contribute. Finally, regardless of predisposing risk factors, women from different population settings may choose or receive different treatment modalities for similarly staged cancers.11,13 It remains unclear whether tumor biology or treatment factor differences drive these population mortality differences. Comparing breast cancer prognostic characteristics might be hypothesis-generating with regard to whether differences in inherent tumor biology drive these population mortality differences. The 21-gene assay (Oncotype DX) predicts the 10-year risk of distant breast cancer recurrence in patients with estrogen receptor-positive (ER-positive), human epidermal growth factor receptor 2 (HER2) negative early-stage breast cancer (EBC) based on testing of tumor tissue.18 Te assay has been commercially available since 2004 in hormone receptor-positive (HR-positive ) breast cancer and is used in clinical practice.19 Recurrence scores on the assay range from 0-100, with lower results correlated with less risk of distant recurrence.18 Patients can be divided into 3 groups based on the assay scores: low, intermediate, or high risk. Te high-risk group (score results, >31) is likely to benefit from chemotherapy, whereas the low-risk group (<18) does not benefit.20-22 Current recommendations for the intermediate-risk group (18-30) include offering chemotherapy,23,24 although the risk reduction from chemotherapy in this group remains uncertain. An ongoing study (TAIL0Rx/PACCT-01) is specifically designed to answer whether chemotherapy benefits women with node-negative HR-positive EBC with an intermediate score result. TAILORx is expected to report results in 2017.25 Differences between rural and urban populations on the basis of recurrence scores have not been reported. Score results may offer insight into prognostic differences between rural and urban women who present with breast cancers of similar stage and receptor-status. Therefore, we retrospectively assessed rural and urban differences by recurrence scores to understand possible causes for rural-urban differences in breast cancer outcomes such as overall breast cancer-associated mortality. Secondary objectives included assessing rural and urban differences in other risk factors as well as therapies received based on recurrence score.