The BMC Medicine published a forum article gathering BC specialists from around the world to discuss the impact on race and ethnicity on diagnostic and treatment disparities and the implications of these inequities for precision oncology. This forum examined BC disparities in the U.S. between different ethnic and racial groups, BC among young women in the UK, the impact of ethnicity on efficacy and toxicity of cyclin-dependent kinase 4/6 inhibitors, and ethnic differences in BRCA mutant BC and PARP (poly [ADP-ribose] polymerase) inhibitors.

The authors discuss structural barriers to health equity in the U.S. and how this impacts BC. In the U.S., it is estimated that 3.1% of all black and 2.5% of all white women will die of BC. The mortality rate for black women exceeds that for Hispanic and Asian women as well. This disparity is thought to be due to an interplay of social determinants of health (SDOH), allostatic load (i.e., an SDOH that describes the effect of a chronic stress state on neural and neuroendocrine responses), tumor biology, access to high-quality care, and enrolment in clinical trials. Women of color experience barriers to mammography, which results in BC being diagnosed at a later stage.

Underuse of adjuvant therapies have been reported in 34% of black, 23% of Hispanic, and 16% of white women. Rate of adjuvant radiation are 48% lower in black women than in non-Hispanic white women. Genetic testing occurs less frequently in women of color.

Women who are diagnosed with BC who are aged younger than age 40 years are at higher risk of germline mutations. Further, only 3% of oncologists are black. Higher allostatic loads are more common in black women and are associated with more advanced BC states, biologically aggressive tumors, and a worse quality of life. Triple-negative BC, a more aggressive form of disease occurs over twice as more often in black women than in white women (21% vs. 10%, respectively).

Younger black and Hispanic women have a higher incidence of hormone receptor-negative BC compared with white women. Further, black women are more likely to have TP53 mutations and less likely to have PIK3CA mutations; the former is treated with chemotherapy and the latter with targeted therapies that have been associated with increased survival. Black women are underrepresented in clinical BC trials with <3% of study subjects belonging to this race, although they make up 12.7% of the population.

Among women aged younger than 50 years, the incidence rate of BC is similar between blacks and whites, although—as a whole for all age groups take together—the incidence is higher for white women than black women. Black women present with higher stage tumors, larger tumors, and are more likely to have metastatic disease at the time of diagnosis. Black women are more often treated with mastectomy because of their aggressive disease; however, this adversely affects their quality of life.

Five-year overall survival is lower in black women (71.1%) than in white women (82.4%). Almost 40% of the excess risk of death from BC in black women was found to be due to health insurance disparities. The reason for differences in inequality of outcomes between the races is multifactorial and includes biology, health behavior, and socioeconomic factors.

Asian women more often have TP53 mutations and are diagnosed with luminal B tumors, which are associated with a worse prognosis and are more resistant to endocrine therapies. Asian women have been underrepresented in trials of cyclin-dependent kinase (CDK) 4 and 6 inhibitor therapy. Efficacy and adverse events may differ between racial and ethnic groups. Asians have been found to have a higher incidence of neutropenia, leukopenia, thrombocytopenia, stomatitis, rash, alanine transaminase elevations, rash, and nasopharyngitis compared with other racial groups in most trials of CDK4/6 inhibitors; however, efficacy was comparable to other groups despite the increase in adverse events. Factors that may contribute to these discrepancies between the groups include differences in CYP3A4, P-glycoprotein, and BC resistance protein activity.

Asian women are usually premenopausal at the time of BC diagnosis with 15% aged younger than 40 years. Germline BRCA1 and/or BRCA2 mutations occur slightly more frequently in Asian women than in other populations. In Korean women, TP53 mutations were reported in 62% of cases with BRCA2 mutation being exclusive with TP53 mutations and co-occurring with BRCA1 mutations. The prevalence of BRCA mutations is higher in estrogen receptor—positive women. This may affect the place in therapy of PARP inhibitors, which have been shown to have clinical activity in somatic and/or germline BRCA-mutated malignancies.

This forum offers pharmacist insight into the different factors that contribute to disparities in the diagnosis and management of BC among various ethnic and racial groups and highlights the unique place of precision medicine in managing this disease state.

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