Immunohistochemical Profile and Molecular Subtype Distribution of Breast Cancer in Libya: A Multi-Laboratory Retrospective Study

Abstract

: Immunohistochemistry (IHC) for estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2), and Ki-67 is the routine surrogate for molecular subtyping of invasive breast cancer, but reference values from Libyan laboratories are scarce. We describe the IHC biomarker profile and molecular subtype distribution of 214 breast cancer reports compiled retrospectively from three Libyan sources (Saleem Laboratory, Benghazi Lab for Medical Analysis, and Benghazi National Cancer Center / other referring sources; 2010–2022, 88.8% dated 2019–2022). ER and PR were scored by the Allred system (0–8) and HER2 by IHC (0/1+/2+/3+); surrogate molecular subtypes were assigned using the post-2011 St Gallen definitions with a 15% Ki-67 cut-off. Patients were predominantly female (170/173 with known sex, 98.3%); known age (n=169) ranged 29–76 years (mean 50.1, median 49), and most reports originated from eastern Libya (172/200 with known location, 86.0%). Among scored reports, ER was strongly positive (Allred 7–8) in 54.1% and PR in 29.5%. HER2 (206 scored) was 0 in 51.9%, 1+ in 20.4%, 2+ (equivocal) in 5.8% and 3+ (positive) in 21.8%. Among 191 reports classifiable by all four markers, luminal B-like was the most frequent subtype (46.1%), followed by luminal A-like (26.2%), triple-negative/basal-like (14.7%) and HER2-overexpression (13.1%); biomarker positivity was broadly consistent across laboratories. This multi-laboratory series provides local reference values for breast cancer IHC and molecular subtype distribution in Libya, dominated by luminal B-like disease and a marked geographic skew toward the east. Standardized IHC reporting and broader geographic sampling are needed for nationally representative estimates.