Clinical Report: Comparing Immunohistochemical and Molecular Breast Cancer Subtyping in African Populations
Overview
This cross-sectional study compared IHC-based breast cancer subtyping with PAM50 molecular classification in 460 Kenyan patients and validated findings in an independent Ghanaian cohort of 451 patients. The supplied study summary reports that adding a proliferation measure—Ki-67 or histologic grade—improved identification of luminal B tumors, which were often classified as luminal A when proliferation was not considered.
Background
Breast cancer is a major cause of cancer-related death among women, and the supplied context reports a 2022 mortality-to-incidence ratio of 55.2% in East Africa, compared with 12.9% in the United States and Canada. In Kenya, breast cancer accounts for more than 25% of cancers diagnosed in women, and more than 80% of patients are not expected to survive five years, according to the context provided. PAM50 classifies tumors into intrinsic molecular subtypes but is constrained in routine use by technical complexity and cost. IHC markers and histologic grade are used as surrogate measures, although the source notes that these approaches have been validated mainly in high-income populations.
Data Highlights
Measure
Finding
Kenyan study cohort
460 patients with pathologically confirmed invasive breast cancer
Kenyan recruitment
Study T: 342 patients recruited at 11 hospitals, 2012–2015; Study G: 118 patients recruited at Kijabe Hospital and Aga Khan University Hospital beginning in 2019
Ghana validation cohort
451 women with invasive breast cancer enrolled in the Ghana Breast Health Study, 2013–2015
Reported luminal B classification in Kenya
Among IHC-defined luminal tumors, the proportion classified as luminal B increased from 12.2% to 41.2% when a proliferation measure was added
East Africa mortality-to-incidence ratio, 2022
55.2%, compared with 12.9% in the United States and Canada
Key Findings
The study assessed concordance between IHC-based subtyping and PAM50 in 460 Kenyan patients and used an independent cohort of 451 Ghanaian patients for validation.
The supplied research summary reports that IHC identified many basal-like tumors, while luminal B tumors were frequently misclassified as luminal A when proliferation markers were omitted.
In Kenya, adding Ki-67 at a threshold of 20% or histologic grade increased the proportion of IHC-defined luminal tumors classified as luminal B from 12.2% to 41.2%, as reported in the web research context.
The research summary states that excluding PR from the minimal IHC panel did not materially reduce concordance, whereas adding a proliferation measure improved agreement.
In the Ghana validation cohort, histologic grade was used as the only proliferation surrogate, according to the supplied research context.
The article context describes PAM50 as classifying tumors into luminal A, luminal B, ERBB2-enriched, basal-like, and normal-like subtypes, while noting its technical and cost constraints for broad implementation.
Clinical Implications
The study addresses whether commonly available IHC markers and histologic grading represent PAM50 subtypes in Kenyan and Ghanaian populations. The supplied research summary reports improved agreement when a proliferation measure is included, and identifies luminal B versus luminal A classification as a source of discordance.
Conclusion
In the African cohorts described, IHC-based classification showed important discordance with PAM50, particularly for luminal A and luminal B tumors when proliferation was not assessed. The supplied findings report improved luminal B classification with Ki-67 or histologic grade and validation in Ghana.
by Shahin Sayed, Li Feng, Hela Koka, Manel Haj Mansour, Difei Wang, Maria Brown, Kristine Jones, Margaret Maina, Veronica Ngundo, Alfred Mburu Githuka, Zaitun Ajuoga, Shaoqi Fan, Amber N. Hurson, Xing Hua, Petra Lenz, Rosemary Wangari Kamau, Beryl Akinyi Ooro, Francis Makokha, Stefan Ambs, Aaron M. Rozeboom, Amy Hutchinson, Belynda Hicks, Mustapha Abubakar, Xiaohong R. Yang
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