Molecular classification of breast cancers using immunohistochemical surrogates; the Sri Lankan experience

Abstract

Background: Breast cancer diagnosis has evolved over the past decades. Today, it is vital to classify breast cancers according to genetic expression. Immunohistochemical surrogates have been identified as a cost-effective routine method to address the genetic diversity of breast cancers.

Aim: To describe the survival pattern of a cohort of breast cancer patients in the Sri Lankan setting, according to the molecular classification using IHC surrogates.

Method: Breast cancer (BC) patients investigated in our laboratory from 2006-2015 were included. Tissue microarrays were constructed using their archived BC tissue. Immunohistochemical assessment of hormone receptors, Her2, Ki67, CK5/6 and EGFR were done. The Pearson chi-square test, Kaplan-Meier model and Cox-regression model were used for analysis.

Results: The study cohort comprised 1122 patients. The complete molecular classification could be performed only for 939 patients with 27.7% -Luminal - A, 10.5% - luminal - B (Her2-), 9.1%-luminal -B (Her2+), 14.6% - Her2 enriched, 9.9% - triple negative and 8.2% - basal-like BC.

Molecular subtypes had a significant association with age (p=0.045), tumour size (p=0.001), Nottingham grade (p<0.000), lymph node stage (p=0.001) and prevalence of lympho-vascular invasion (p=0.003). Five-year BC specific survival (BCSS) of the study cohort was 75.5% (92.3% in luminal-A, 54.2% in Her2-enriched, 72.2% in triple-negative and 64.4% in basal-like groups; p<0.001). The molecular subtype (p<0.000, p=0.003) and lymph node stage (p<0.001) had an independent effect on the BCSS and RFS respectively.

Conclusion: The molecular classification using immunohistochemical surrogates, classify breast cancers into clinically useful groups with distinctively different survival rates.