Women of sub-Saharan African descent have disproportionately higher incidence of triple-negative breast cancer (TNBC) and TNBC-specific mortality across all populations. Population studies show racial differences in TNBC biology, including higher prevalence of basal-like and quadruple-negative subtypes in African Americans (AA). However, previous investigations relied on self-reported race (SRR) of primarily U.S. populations. Due to heterogeneous genetic admixture and biological consequences of social determinants, the true association of African ancestry with TNBC biology is unclear. To address this, we conducted RNA sequencing on an international cohort of AAs, as well as West and East Africans with TNBC. Using comprehensive genetic ancestry estimation in this African-enriched cohort, we found expression of 613 genes associated with African ancestry and 2,000+ associated with regional African ancestry. A subset of African-associated genes also showed differences in normal breast tissue. Pathway enrichment and deconvolution of tumor cellular composition revealed that tumor-associated immunologic profiles are distinct in patients of African descent. Significance: Our comprehensive ancestry quantification process revealed that ancestry-associated gene expression profiles in TNBC include population-level distinctions in immunologic landscapes. These differences may explain some differences in race–group clinical outcomes. This study shows the first definitive link between African ancestry and the TNBC immunologic landscape, from an African-enriched international multiethnic cohort. See related commentary by Hamilton et al., p. 2496. This article is highlighted in the In This Issue feature, p. 2483

Poly (ADP-ribose) polymerase inhibitors (PARPi) are used for patients with BRCA1/2 mutations, but patients with other mutations may benefit from PARPi treatment. Another mutation that is present in more cancers than BRCA1/2 is mutation to the TP53 gene. In 2D breast cancer cell lines, mutant p53 (mtp53) proteins tightly associate with replicating DNA and Poly (ADP-ribose) polymerase (PARP) protein. Combination drug treatment with the alkylating agent temozolomide and the PARPi talazoparib kills mtp53 expressing 2D grown breast cancer cell lines. We evaluated the sensitivity to the combination of temozolomide plus PARPi talazoparib treatment to breast and lung cancer patient-derived tumor organoids (PDTOs). The combination of the two drugs was synergistic for a cytotoxic response in PDTOs with mtp53 but not for PDTOs with wtp53. The combination of talazoparib and temozolomide induced more DNA double-strand breaks in mtp53 expressing organoids than in wild-type p53 expressing organoids as shown by increased γ-H2AX protein expression. Moreover, breast cancer tissue microarrays (TMAs) showed a positive correlation between stable p53 and high PARP1 expression in sub-groups of breast cancers, which may indicate sub-classes of breast cancers sensitive to PARPi therapy. These results suggest that mtp53 could be a biomarker to predict response to the combination of PARPi talazoparib-temozolomide treatment.

Precision medicine approaches to cancer treatment aim to exploit genomic alterations that are specific to individual patients to tailor therapeutic strategies. Yet, some targetable genes and pathways are essential for tumor cell viability even in the absence of direct genomic alterations. In underrepresented populations, the mutational landscape and determinants of response to existing therapies are poorly characterized because of limited inclusion in clinical trials and studies. One way to reveal tumor essential genes is with genetic screens. Most screens are conducted on cell lines that bear little resemblance to patient tumors, after years of culture under nonphysiologic conditions. To address this problem, we aimed to develop a CRISPR screening pipeline in three-dimensionally grown patient-derived tumor organoid (PDTO) models. A breast cancer PDTO biobank that focused on underrepresented populations, including West African patients, was established and used to conduct a negative-selection kinome-focused CRISPR screen to identify kinases essential for organoid growth and potential targets for combination therapy with EGFR or MEK inhibitors. The screen identified several previously unidentified kinase targets, and the combination of FGFR1 and EGFR inhibitors synergized to block organoid proliferation. Together, these data demonstrate the feasibility of CRISPR-based genetic screens in patient-derived tumor models, including PDTOs from underrepresented patients with cancer, and identify targets for cancer therapy. Significance: Generation of a breast cancer patient-derived tumor organoid biobank focused on underrepresented populations enabled kinome-focused CRISPR screening that identified essential kinases and potential targets for combination therapy with EGFR or MEK inhibitors. See related commentary by Trembath and Spanheimer, p. 407

PURPOSE: Delivering high-quality cancer care to patients through a multidisciplinary team (MDT) care approach remains a challenge, particularly in low- and middle-income countries characterized by fragmented health systems and limited human resources for cancer care. City Cancer Challenge (C/Can) is supporting cities in low- and middle-income countries as they work to improve access to equitable quality cancer care. C/Can has developed an innovative methodology to address the MDT gap, piloted in four cities—Asunciòn, Cali, Kumasi, and Yangon. METHODS: Collaborating with a network of partners, C/Can and ASCO have developed a package of technical cooperation support focusing on two priority areas that have emerged as core needs: first developing consensus-based, city-wide patient management guidelines for the most common cancers and second, building capacity for the implementation of MDTs in institutions providing cancer care in the city. RESULTS: The real-time application of C/Can's MDT approach in Cali and Asuncion underlined the importance of engaging the right stakeholders early on and embedding MDT guidelines in local and national regulatory frameworks to achieve their sustainable uptake. The results in Cali and Asuncion were essential for informing the process in Yangon, asserting the clear benefits of city-to-city knowledge exchange. Finally, the global COVID-19 pandemic prompted a rapid adaptation of the methodology from an in-person to virtual format; the unexpected success of the virtual program in Kumasi has led to its application in subsequent C/Can cities. CONCLUSION: The application of C/Can's methodology in this first set of cities has reinforced not only the importance of both resource appropriate guidelines and a highly trained health workforce but also the need for commitment to work across institutions and disciplines.

PURPOSE: The WHO's Global Breast Cancer Initiative (GBCI) described three key performance indicators (KPIs) to reduce breast cancer deaths worldwide. We assessed the management of breast cancer in Ghana against the GBCI KPIs to inform necessary steps for system-wide improvement. METHODS: We reviewed patients diagnosed with breast cancer in 2021 calendar year at Ghana's second largest tertiary hospital. Relevant data were extracted from the electronic medical records to determine the stage of breast cancer at diagnosis, duration to confirm diagnosis from initial presentation, and proportion of patients completing recommended treatment without abandonment. Data were presented as descriptive statistics and compared with GBCI KPI benchmarks. RESULTS: Of 319 patients undergoing biopsy of suspicious breast lesions, 243 were diagnosed with breast cancer. Most (98.7%) were female, with a median age of 49 years and median symptom duration of 24 weeks. Diagnosis was confirmed for all patients within 31 days of initial presentation. Only 22 of 214 patients (10.3%) undergoing staging were diagnosed as early breast cancer (stage I or II), 50% at stage III, and 39.3% at stage IV. Forty-five of 139 patients (32.4%) initiating recommended treatment completed without abandonment, and 45 of 243 patients (18.5%) with a confirmed breast cancer completed recommended treatment without abandonment. CONCLUSION: Ghana met the GBCI KPI for timely diagnosis (80%). Our findings provide baseline data for planning system-wide improvements toward the GBCI's goal of reducing breast cancer mortality by 2.5% annually.

Accessory breasts denote the formation of extra breast tissue along the milk line, and are known to be more prevalent among Black and Asian populations, affecting both genders. This first-ever study aimed to determine the genetic aetiology of accessory breasts in a multiplex family, where all female siblings present with bilateral accessory breasts. The study also ascertained secondary findings (SFs) responsible for comorbidities. Clinical data and saliva samples were obtained from all family members. Ultrasound and histopathology confirmed the diagnosis. Whole-exome sequencing was conducted on DNA samples obtained from the saliva, with variant calling conducted utilising the Sentieon workflow. Variant classification was based on American College of Medical Genetics and Genomics guidelines. After segregation analysis, 12 candidate genes emerged. Among these, PRSS50 and FANCC emerged as top candidates, being implicated in breast diseases. However, two variants in FANCC (c.360del; p.His120GlnfsTer24 and c.355_358del; p.Ser119IlefsTer24) were selected as the most probable causal variants because of the role of this gene in hereditary breast and ovarian cancer syndromes. The remaining ten genes were reported as potentially accounting for comorbidities segregating with accessory breasts. Reported SFs involve TTR and RYR1. In conclusion, pathogenic variants in FANCC cause familial accessory breasts. These novel observations impact pathophysiology, genetic counselling, and personalised medicine.