Oncotype DX recurrence score implications for disparities in chemotherapy and breast cancer mortality in Georgia

Development and validation of a clinical breast cancer tool for accurate prediction of recurrence

Given high costs of Oncotype DX (ODX) testing, widely used in recurrence risk assessment for early-stage breast cancer, studies have predicted ODX using quantitative clinicopathologic variables. However, such models have incorporated only small cohorts. Using a cohort of patients from the National Cancer Database (NCDB, n = 53,346), we trained machine learning models to predict low-risk (0-25) or high-risk (26-100) ODX using quantitative estrogen receptor (ER)/progesterone receptor (PR)/Ki-67 status, quantitative ER/PR status alone, and no quantitative features. Models were externally validated on a diverse cohort of 970 patients (median follow-up 55 months) for accuracy in ODX prediction and recurrence. Comparing the area under the receiver operating characteristic curve (AUROC) in a held-out set from NCDB, models incorporating quantitative ER/PR (AUROC 0.78, 95% CI 0.77-0.80) and ER/PR/Ki-67 (AUROC 0.81, 95% CI 0.80-0.83) outperformed the non-quantitative model (AUROC 0.70, 95% CI 0.68-0.72). These results were preserved in the validation cohort, where the ER/PR/Ki-67 model (AUROC 0.87, 95% CI 0.81-0.93, p = 0.009) and the ER/PR model (AUROC 0.86, 95% CI 0.80-0.92, p = 0.031) significantly outperformed the non-quantitative model (AUROC 0.80, 95% CI 0.73-0.87). Using a high-sensitivity rule-out threshold, the non-quantitative, quantitative ER/PR and ER/PR/Ki-67 models identified 35%, 30% and 43% of patients as low-risk in the validation cohort. Of these low-risk patients, fewer than 3% had a recurrence at 5 years. These models may help identify patients who can forgo genomic testing and initiate endocrine therapy alone. An online calculator is provided for further study.

Race, Gene Expression Signatures, and Clinical Outcomes of Patients With High-Risk Early Breast Cancer

Importance

There has been little consideration of genomic risk of recurrence by breast cancer subtype despite evidence of racial disparities in breast cancer outcomes.

Objective

To evaluate associations between clinical trial end points, namely pathologic complete response (pCR) and distant recurrence-free survival (DRFS), and race and examine whether gene expression signatures are associated with outcomes by race.

Design, Setting, and Participants

This retrospective cohort study used data from the Investigation of Serial Studies to Predict Your Therapeutic Response With Imaging and Molecular Analysis 2 (I-SPY 2) multicenter clinical trial of neoadjuvant chemotherapy with novel agents and combinations for patients with previously untreated stage II/III breast cancer. Analyses were conducted of associations between race and short- and long-term outcomes, overall and by receptor subtypes, and their association with 28 expression biomarkers. The trial enrolled 990 female patients between March 30, 2010, and November 5, 2016, with a primary tumor size of 2.5 cm or greater and clinical or molecular high risk based on MammaPrint or hormone receptor (HR)-negative/ERBB2 (formerly HER2 or HER2/neu)-positive subtyping across 9 arms. This data analysis was performed between June 10, 2021, and October 20, 2022.

Exposure

Race, tumor receptor subtypes, and genomic biomarker expression of early breast cancer.

Main Outcomes and Measures

The primary outcomes were pCR and DRFS assessed by race, overall, and by tumor subtype using logistic regression and Cox proportional hazards regression models. The interaction between 28 expression biomarkers and race, considering pCR and DRFS overall and within subtypes, was also evaluated.

Results

The analytic sample included 974 participants (excluding 16 self-reporting as American Indian or Alaska Native, Native Hawaiian or Other Pacific Islander, or multiple races due to small sample sizes), including 68 Asian (7%), 120 Black (12%), and 786 White (81%) patients. Median (range) age at diagnosis was 47 (25-71) years for Asian, 49 (25-77) for Black, and 49 (23-73) years for White patients. The pCR rates were 32% (n = 22) for Asian, 30% for Black (n = 36), and 32% for White (n = 255) patients (P = .87). Black patients with HR-positive/ERBB2-negative tumors not achieving pCR had significantly worse DRFS than their White counterparts (hazard ratio, 2.28; 95% CI, 1.24-4.21; P = .01), with 5-year DRFS rates of 55% (n = 32) and 77% (n = 247), respectively. Black patients with HR-positive/ERBB2-negative tumors, compared with White patients, had higher expression of an interferon signature (mean [SD], 0.39 [0.87] and -0.10 [0.99]; P = .007) and, compared with Asian patients, had a higher mitotic score (mean [SD], 0.07 [1.08] and -0.69 [1.06]; P = .01) and lower estrogen receptor/progesterone receptor signature (mean [SD], 0.31 [0.90] and 1.08 [0.95]; P = .008). A transforming growth factor β signature had a significant association with race relative to pCR and DRFS, with a higher signature associated with lower pCR and worse DRFS outcomes among Black patients only.

Conclusions and Relevance

The findings show that women with early high-risk breast cancer who achieve pCR have similarly good outcomes regardless of race, but Black women with HR-positive/ERBB2-negative tumors without pCR may have worse DRFS than White women, highlighting the need to develop and test novel biomarker-informed therapies in diverse populations.

Differential distribution of actual and surrogate oncotype DX recurrence scores in breast cancer patients by age, menopausal status, race, and body mass index

PURPOSE

The Oncotype DX Recurrence Score (RS) is a widely used prognostic tool for estrogen receptor-positive breast cancer patients. Multiple surrogate models can predict RS with good accuracy. In this study we aimed to determine whether the RS and two surrogate indices were differentially distributed by age, menopausal status, race, and body mass index (BMI).

METHODS

516 breast cancer cases treated at a single institution were analyzed. Epidemiologic data, RS, tumor size, grade, and biomarker data were abstracted. Breast Cancer Prognostic Score (BCPS) and modified Magee equation 2 were used to calculate surrogate RS. Patients were stratified into different groups based on age, menopausal status, race, BMI, or a combination of strata. Mean and standard deviation were calculated for each group/subgroup.

RESULTS

Age below median (< 63) was associated with higher RS, especially in obese and Black patients. RS was also higher in obese and Black patients in the premenopausal subgroup. Black patients had a higher RS compared to White women in the premenopausal and non-obese subgroups. BMI < 30 was associated with higher RS, especially in older, postmenopausal, and Black patients. Some of these observations were replicated by the two surrogate models. The surrogate recurrence scores were higher in the younger age group, in non-obese older/postmenopausal women, and in younger/premenopausal obese individuals.

CONCLUSIONS

Higher RS was observed in younger and premenopausal breast cancer patients, especially among the Black and obese subgroups, and in non-obese patients, especially among Black and older/postmenopausal women, suggesting more aggressive disease in these subgroups. Some statistical differences could be replicated by both surrogate models, suggesting that they may have utility in breast cancer epidemiology studies that do not have access to Oncotype DX RS or patient outcome data.

Predicting Chemotherapy Benefit across Different Races in Early-Stage Breast Cancer Patients Using the Oncotype DX Score

BACKGROUND

Oncotype DX assay, a multigene molecular test, has been widely used to stratify relapse risk and guide chemotherapy treatment in breast cancer. However, the optimal threshold of the Oncotype DX score in predicting chemotherapy benefit and its racial variation has not been investigated.

METHODS

In this study, we apply a random forest survival model to the SEER-Oncotype cohort data (Surveillance, Epidemiology, and End Results with Oncotype DX test information for breast cancer patients) and determine chemotherapy benefit thresholds in early-stage, estrogen-receptor-positive (ER+), and HER2-negative (HER2-) patients of different races.

RESULTS

Our results indicate that early-stage ER+, HER2-, and LN-/LN+ patients may benefit from receiving chemotherapy at a lower Oncotype DX score than current guidelines (Recurrence Score, RS > 25 or RS > 30) suggest. According to the estimated chemotherapy sensitivity thresholds from our models, 2.05-2.72-fold more lymph-node-negative (LN-) and 2.08-5.02-fold more lymph-node-positive (LN+) patients who may not currently be recommended for chemotherapy by their Oncotype DX test result may actually have the potential to benefit from chemotherapy. Furthermore, our models indicate a racial difference in chemotherapy benefit: white, black, and Asian women with early-stage ER+/LN- tumors benefit from chemotherapy when their Oncotype DX scores are greater than 19.9, 37.2, and 18.0, respectively.

CONCLUSIONS

Our study provides a method for calibrating multigene molecular tests to help guide treatment decisions in racially and ethnically diverse patients with cancer. Specifically, we identify key chemotherapy sensitivity thresholds for the Oncotype DX recurrence score test in breast cancer patients and provide evidence that certain patients may benefit from receiving chemotherapy at a lower threshold than the current clinical guidelines suggest.

Survival Disparities in US Black Compared to White Women with Hormone Receptor Positive-HER2 Negative Breast Cancer

Black women in the US have significantly higher breast cancer mortality than White women. Within biomarker-defined tumor subtypes, disparate outcomes seem to be limited to women with hormone receptor positive and HER2 negative (HR+/HER2-) breast cancer, a subtype usually associated with favorable prognosis. In this review, we present data from an array of studies that demonstrate significantly higher mortality in Black compared to White women with HR+/HER2-breast cancer and contrast these data to studies from integrated healthcare systems that failed to find survival differences. Then, we describe factors, both biological and non-biological, that may contribute to disparate survival in Black women.

Diversity, Equity, and Inclusion in Clinical Trials

Minority groups are vastly underrepresented in clinical trial participants and leadership. Because these studies provide innovative and revolutionary treatment options to patients with cancer and have the potential to extend survival, it is imperative that public and private stakeholders, as well as hospital and clinical trial leadership, prioritize equity and inclusion of diverse populations in clinical trial development and recruitment strategies. Achieving equity in clinical trials could be an important step in reducing the overall cancer burden and mortality disparities in vulnerable populations.

Understanding Racial and Ethnic Inequities in Uptake and Outcomes Following Multigene Prognostic Testing in Early Breast Cancer: The Promise of Real-World Data

In the past decades, multigene prognostic testing, such as Oncotype DX (ODX), has been increasingly used to inform treatment decisions for patients with early-stage breast cancer. This advance in precision oncology has increased existing concerns about differential access to genomic testing across racial and ethnic groups. The investigation by Moore and colleagues, analyzing real-world data from the National Cancer Database, shows that patients of color with breast cancer were less likely to receive ODX testing and Black patients were more likely to have a high risk Recurrence Score (RS) compared with White patients. This study emphasizes that the appropriate adoption of ODX testing is critical to promote equitable cancer care for patients with breast cancer. The reported associations on overall survival across specific racial and ethnic groups provided here give additional insight to the known associations between the ODX RS and outcomes of distant recurrence and cancer-specific mortality. Analyses of contemporary, real-world data from diverse populations with long-term follow-up should continue to keep pace with the expansion of precision breast cancer care to better understand and mitigate potentially widening inequities in genomic testing. See related article by Moore et al., p. 821.

Oncotype DX Risk Recurrence Score and Total Mortality for Early-Stage Breast Cancer by Race/Ethnicity

BACKGROUND

Oncotype DX recurrence score (ODX RS) is a prognostic biomarker for early-stage, node-negative, estrogen receptor-positive (ER+) breast cancer. Whether test uptake, associated factors, and the test's prognostic values differ by race/ethnicity is unknown.

METHODS

From the National Cancer Database, 2010-2014, we identified 227,259 early-stage ER+, node-negative breast cancer cases. Logistic regression was used to examine ODX RS uptake and associated factors among non-Hispanic White (White), non-Hispanic Black (Black), Hispanic, and Asian American patients. Cox regression was used to estimate hazard ratios (HR) and 95% confidence intervals (CI) for overall mortality with ODX RS by race/ethnicity.

RESULTS

White patients were more likely to receive an ODX RS test compared with Black, Hispanic, and Asian American patients (36.7%, 32.8%, 31.6%, and 35.5%, respectively; P < 0.001). Disparities persisted after adjustments for demographics, clinical characteristics, and access-to-care, with rate ratios of 0.87 (95% CI, 0.85-0.88), 0.82 (95% CI, 0.80-0.85), and 0.89 (95% CI, 0.87-0.92), respectively, for Black, Hispanic, and Asian American compared with White patients. Black patients had higher proportions of high-risk scores (≥26) compared with White, Hispanic, and Asian American patients (19.1%, 14.0%, 14.2%, and 15.6%, respectively; P < 0.0001). ODX RS was predictive for total mortality across all races/ethnicities, particularly younger patients (<50). No significant race/ethnicity interactions were observed.

CONCLUSIONS

Although ODX RS uptake and risk distribution varied by race/ethnicity, ODX RS was prognostic for mortality across groups.

IMPACT

These findings emphasize the importance of developing strategies to increase ODX RS uptake among racial/ethnic minorities and call for more investigations on potential racial/ethnic differences in breast cancer biology. See related commentary by Wang et al., p. 704.

Receipt of Guideline-Concordant Care Does Not Explain Breast Cancer Mortality Disparities by Race in Metropolitan Atlanta

BACKGROUND

Racial disparities in breast cancer mortality in the United States are well documented. Non-Hispanic Black (NHB) women are more likely to die of their disease than their non-Hispanic White (NHW) counterparts. The disparity is most pronounced among women diagnosed with prognostically favorable tumors, which may result in part from variations in their receipt of guideline care. In this study, we sought to estimate the effect of guideline-concordant care (GCC) on prognosis, and to evaluate whether receipt of GCC modified racial disparities in breast cancer mortality.

PATIENTS AND METHODS

Using the Georgia Cancer Registry, we identified 2,784 NHB and 4,262 NHW women diagnosed with a stage I-III first primary breast cancer in the metropolitan Atlanta area, Georgia, between 2010 and 2014. Women were included if they received surgery and information on their breast tumor characteristics was available; all others were excluded. Receipt of recommended therapies (chemotherapy, radiotherapy, endocrine therapy, and anti-HER2 therapy) as indicated was considered GCC. We used Cox proportional hazards models to estimate the impact of receiving GCC on breast cancer mortality overall and by race, with multivariable adjusted hazard ratios (HRs).

RESULTS

We found that NHB and NHW women were almost equally likely to receive GCC (65% vs 63%, respectively). Failure to receive GCC was associated with an increase in the hazard of breast cancer mortality (HR, 1.74; 95% CI, 1.37-2.20). However, racial disparities in breast cancer mortality persisted despite whether GCC was received (HRGCC: 2.17 [95% CI, 1.61-2.92]; HRnon-GCC: 1.81 [95% CI, 1.28-2.91] ).

CONCLUSIONS

Although receipt of GCC is important for breast cancer outcomes, racial disparities in breast cancer mortality did not diminish with receipt of GCC; differences in mortality between Black and White patients persisted across the strata of GCC.

Association of Insulin Resistance and Higher Oncotype DX™ Recurrence Score

BACKGROUND

Black women with breast cancer have a worse overall survival compared with White women; however, no difference in Oncotype DX™ (ODX) recurrence scores has been observed to explain this health disparity. Black women are also disproportionately affected by insulin resistance. We evaluated whether insulin resistance is associated with a higher ODX recurrence score and whether there is a difference between White and Black women to explain disparate clinical outcomes.

METHODS

A subgroup analysis of patients in a multi-institutional cross-sectional study evaluating differences in insulin resistance between White and Black women was performed. Women diagnosed with a new hormone receptor-positive, HER2/neu-negative breast cancer with an ODX recurrence score were identified. Fasting blood glucose and insulin measurements were used to calculate the homeostatic model assessment of insulin resistance (HOMA-IR) score, a method for assessing insulin resistance, and compared against ODX scores.

RESULTS

Overall, 412 women (358 White women, 54 Black women) were identified. Compared with White women, Black women had a higher body mass index (30 vs. 26 kg/m², p < 0.0001), higher HOMA-IR score (2.4 vs. 1.4, p = 0.004), and more high-grade tumors (30% vs. 16%, p = 0.01). There was a direct positive association with an increasing ODX score and HOMA-IR (p = 0.014). On subset analysis, this relationship was seen in White women (p = 0.005), but not in Black women (p = 0.55).

CONCLUSION

In women with newly diagnosed breast cancer, increasing insulin resistance is associated with a higher recurrence score; however, this association was not present in Black women. This lack of association may be due to the small number of Black women in the cohort, or possibly a reflection of a different biological disease process of the patient's tumor.

Lymphovascular invasion, race, and the 21-gene recurrence score in early estrogen receptor-positive breast cancer

Lymphovascular invasion (LVI) and Black race are associated with poorer prognosis in early breast cancer (EBC). We evaluated the association between LVI and race, and whether LVI adds prognostic benefit to the 21-gene recurrence score (RS) in EBC. Women with ER+ HER2- EBC measuring up to 5 cm, with 0-3 involved axillary nodes, diagnosed between 1 January 2010 and 1 January 2014, who underwent surgery as first treatment and had available RS, were identified in the NCDB database. Bivariate associations between two categorical variables were examined using chi-square test. Multivariate Cox proportional hazards model were used to assess the association of LVI, race, and other covariates with overall survival (OS). 77,425 women, 65,018 node-negative (N0), and 12,407 with 1-3 positive (N+) nodes, were included. LVI was present in 12.7%, and associated with poor grade, RS 26-100, and N+ (all p < 0.0001), but not Black race. In multivariate analysis, LVI was associated with worse OS in N0 [HR 1.37 (95% CI 1.27, 1.57], but not N+ EBC. LVI was associated with worse OS in N0 patients with RS 11-25 [HR 1.31 (95% CI 1.09, 1.57)] and ≥26 [HR 1.58 (95% CI 1.30, 1.93)], but not RS 0-10. No interaction between LVI and chemotherapy benefit was seen. Black race was associated with worse OS in N0 (HR 1.21, p = 0.009) and N+ (HR 1.37, p = 0.015) disease. LVI adds prognostic information in ER+, HER2-, N0 BCA with RS 11-100, but does not predict chemotherapy benefit. Black race is associated with worse OS, but not LVI.

Association of Race/Ethnicity and the 21-Gene Recurrence Score With Breast Cancer-Specific Mortality Among US Women

Importance

Given the widespread use of the 21-gene recurrence score for identifying candidates for adjuvant chemotherapy, it is important to examine the performance of the Oncotype DX Breast Recurrence Score test in diverse patient populations to validate this approach for tailoring treatment in women in racial/ethnic minority groups.

Objective

To examine whether breast cancer-specific mortality for women with hormone-dependent breast cancer differs by race/ethnicity across risk categories defined by the Oncotype DX Breast Recurrence Score test and whether the prognostic accuracy of the 21-gene recurrence score differs by race/ethnicity.

Design, Setting, and Participants

This retrospective, population-based cohort study used the Surveillance, Epidemiology, and End Results Oncotype DX 2004-2015 database to obtain breast cancer-specific survival data on US women 18 years and older who were diagnosed with first primary stage I to III, estrogen receptor-positive breast cancer between January 1, 2004, and December 31, 2015, and had tumor testing through the Genomic Health Clinical Laboratory. Data were analyzed from April 20 to September 27, 2020.

Main Outcomes and Measures

The primary outcome was breast cancer-specific mortality among women from different racial/ethnic groups stratified by the 21-gene recurrence score risk categories. Secondary analyses compared the prognostic accuracy of the recurrence score among the different racial/ethnic groups.

Results

A total of 86 033 patients with breast cancer (mean [SD] age, 57.6 [10.6] years) with Oncotype DX Breast Recurrence Score test information were available for the analysis, including 64 069 non-Hispanic White women (74.4%), 6719 non-Hispanic Black women (7.8%), 7944 Hispanic women (9.2%), 6950 Asian/Pacific Islander women (8.0%), and 351 American Indian/Alaska Native women (0.4%). Black women were significantly more likely than non-Hispanic White women to have a recurrence score greater than 25 (17.7% vs 13.7%; P < .001). Among women with axillary node-negative tumors, competing risk models adjusted for age, tumor characteristics, and treatment found higher breast cancer-specific mortality for Black compared with non-Hispanic White women within each recurrence score risk stratum, with subdistribution hazard ratios of 2.54 (95% CI, 1.44-4.50) for Black women with recurrence scores of 0 to 10, 1.64 (95% CI, 1.23-2.18) for Black women with recurrence scores of 11 to 25, and 1.48 (95% CI, 1.10-1.98) for Black women with scores greater than 25. The prognostic accuracy of the recurrence score was significantly lower for Black women, with a C index of 0.656 (95% CI, 0.592-0.720) compared with 0.700 (95% CI, 0.677-0.722) (P = .002) for non-Hispanic Whites.

Conclusions and Relevance

In this cohort study, Black women in the US were more likely to have a high-risk recurrence score and to die of axillary node-negative breast cancer compared with non-Hispanic White women with comparable recurrence scores. The Oncotype DX Breast Recurrence Score test has lower prognostic accuracy in Black women, suggesting that genomic assays used to identify candidates for adjuvant chemotherapy may require model calibration in populations with greater racial/ethnic diversity.

Neighborhood-Level Redlining and Lending Bias Are Associated with Breast Cancer Mortality in a Large and Diverse Metropolitan Area

BACKGROUND

Structural inequities have important implications for the health of marginalized groups. Neighborhood-level redlining and lending bias represent state-sponsored systems of segregation, potential drivers of adverse health outcomes. We sought to estimate the effect of redlining and lending bias on breast cancer mortality and explore differences by race.

METHODS

Using Georgia Cancer Registry data, we included 4,943 non-Hispanic White (NHW) and 3,580 non-Hispanic Black (NHB) women with a first primary invasive breast cancer diagnosis in metro-Atlanta (2010-2014). Redlining and lending bias were derived for census tracts using the Home Mortgage Disclosure Act database. We calculated hazard ratios and 95% confidence intervals (CI) for the associations of redlining, lending bias on breast cancer mortality and estimated race-stratified associations.

RESULTS

Overall, 20% of NHW and 80% of NHB women lived in redlined census tracts, and 60% of NHW and 26% of NHB women lived in census tracts with pronounced lending bias. Living in redlined census tracts was associated with a nearly 1.60-fold increase in breast cancer mortality (hazard ratio = 1.58; 95% CI, 1.37-1.82) while residing in areas with substantial lending bias reduced the hazard of breast cancer mortality (hazard ratio = 0.86; 95% CI, 0.75-0.99). Among NHB women living in redlined census tracts, we observed a slight increase in breast cancer mortality (hazard ratio = 1.13; 95% CI, 0.90-1.42); among NHW women the association was more pronounced (hazard ratio = 1.39; 95% CI, 1.09-1.78).

CONCLUSIONS

These findings underscore the role of ecologic measures of structural racism on cancer outcomes.

IMPACT

Place-based measures are important contributors to health outcomes, an important unexplored area that offers potential interventions to address disparities.

Genomic expression assay testing among American Indian and Alaska Native women with breast cancer

BACKGROUND

Breast cancer is one of the most common causes of cancer mortality for all women, including American Indian and Alaska Native (AI/AN) women. The use of the 21-gene recurrence score (RS) appears to be predictive of the benefit of chemotherapy for women with estrogen receptor (ER)-positive breast cancer. The objective of the current study was to compare RS testing between AI/AN and non-Hispanic White (NHW) women with breast cancer.

METHODS

The Surveillance, Epidemiology, and End Results program was used to identify women with ER-positive breast cancer from 2004 through 2015. Multivariable logistic regression was used to evaluate factors associated with RS use, with high-risk RS, and with chemotherapy use among those with a high-risk RS.

RESULTS

A total of 363,387 NHW patients and 1951 AI/AN patients with ER-positive breast cancer were identified. AI/AN women were found to be less likely to undergo RS testing and, when tested, were more likely to have a high-risk RS. In the multivariable logistic regression analysis, AI/AN women were found to be significantly more likely to have a high-risk RS (odds ratio,1.28; 95% confidence interval, 1.01-1.66). Among untested women, chemotherapy use was higher for AI/AN women; however, the use of chemotherapy was not found to be significantly different between the groups with a high-risk RS. Using Cox proportional hazards models, AI/AN race was found to be significantly associated with worse overall survival.

CONCLUSIONS

AI/AN women were less likely to undergo RS testing compared with NHW women and were more likely to have a high-risk RS. Reversing the disparity in genomic expression assay testing is critical to ensure guideline-based breast cancer treatment and improve survival rates for AI/AN women with breast cancer.

Patient and physician factors associated with Oncotype DX and adjuvant chemotherapy utilization for breast cancer patients in New Hampshire, 2010-2016

BACKGROUND

Oncotype DX® (ODX) is used to assess risk of disease recurrence in hormone receptor positive, HER2-negative breast cancer and to guide decisions regarding adjuvant chemotherapy. Little is known about how physician factors impact treatment decisions. The purpose of this study was to examine patient and physician factors associated with ODX testing and adjuvant chemotherapy for breast cancer patients in New Hampshire.

METHODS

We examined New Hampshire State Cancer Registry data on 5630 female breast cancer patients diagnosed from 2010 to 2016. We performed unadjusted and adjusted hierarchical logistic regression to identify factors associated with a patient's receipt of ODX, being recommended and receiving chemotherapy, and refusing chemotherapy. We calculated intraclass correlation coefficients (ICCs) to examine the proportion of variance in clinical decisions explained by between-physician and between-hospital variation.

RESULTS

Over the study period, 1512 breast cancer patients received ODX. After adjustment for patient and tumor characteristics, we found that patients seen by a male medical oncologist were less likely to be recommended chemotherapy following ODX (OR = 0.50 (95% CI = 0.34-0.74), p < 0.01). Medical oncologists with more clinical experience (reference: less than 10 years) were more likely to recommend chemotherapy (20-29 years: OR = 4.05 (95% CI = 1.57-10.43), p < 0.01; > 29 years: OR = 4.48 (95% CI = 1.68-11.95), p < 0.01). A substantial amount of the variation in receiving chemotherapy was due to variation between physicians, particularly among low risk patients (ICC = 0.33).

CONCLUSIONS

In addition to patient clinicopathologic characteristics, physician gender and clinical experience were associated with chemotherapy treatment following ODX testing. The significant variation between physicians indicates the potential for interventions to reduce variation in care.