Molecular subtype characterization of primary breast cancer at the university teaching hospital, Lusaka Zambia.

Breast cancer is the second most common cancer in women in Zambia. It has been established that Oestrogen Receptor (ER), Progesterone Receptor (PR) and Human Epidermal Growth Factor Receptor 2 (HER2) are important markers for treatment and prognosis of breast cancer. Treatment has now become targeted and depends on the molecular subtype. However, at University Teaching Hospitals (UTHs) routine testing for ER, PR and HER2 is not done resulting in patients receiving suboptimal treatment. The aims of this study were to determine the age distribution of breast cancer patients, to classify these cancers according to their histologic type and grade and to molecular classify them as Luminal A, Luminal B, HER2 type and TNBC using ER, PR and HER2 immunohistochemistry (IHC). A total of 68 paraffin embedded breast biopsies from female adults with a histologic diagnosis of breast cancer between 2016 and 2018 were evaluated using standard IHC in this laboratory based cross sectional study. Allred scoring and CAP/ASCO guidelines were used to determine ER/PR and HER2 status, which were considered valid only in the presence of positive controls. Luminal A (Lum A) cancers were defined as ER+/PR+/HER- with a Nottingham mitotic score of 1 while mitotic scores of 2 or 3 were classified as Luminal B (Lum B). HER2 type was defined as any HER2+ (>10%, 3+), and triple negative as ER-/PR-/HER2- (TNBC). FISH was not available and so equivocal HER2 were considered negative. Data was collected for 68 patients, ranging in age from 29-93 years (average and Median 51.3 and 51years respectively). More than half of the cases were ER and/or PR positive (61.8%). However only 13.2% of the tumors examined were the least aggressive Luminal A subtype. 48.5% were of the Luminal B subtype followed by TNBC (29.4%) and the aggressive HER2
type was only seen in 8.8% of the cases. Invasive ductal carcinoma (NOS) was the most common histologic type and majority of tumors were grade 2. Data was analyzed using SPSS version 22 and Chi-square test was done for association between age and dependent variables, all analyzed at 95% confidence interval and p-values <0.05 were considered significant. The study demonstrated breast cancer heterogeneity at UTHs. We therefore recommend a routine
ER, PR and HER2 IHC panel for breast cancer in selection of patients for targeted therapy