Background: Breast cancer (BC) is one of the most common malignancies and a foremost health issue throughout world. BC accounted for 23.1% of cancer cases diagnosed in Oman in 2009. BC is a heterogeneous disease, and immuno-histochemical (IHC) markers are used to further classify it into distinct subtypes, which are biologically discrete and display different behaviors. IHC testing of the estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor-2 (Her-2); can sub-classify BC into 4 principal molecular subtypes. These subtypes are luminal A (ER+ and/or PR+, HER2-), luminal B (ER+ and/or PR+, HER2+), basal like (BCL - ER-, PR-, HER2-), and Her2/neu (ER-, PR-, HER2+). Previous studies have shown preliminary evidence and high probabilities of molecular differences across ethnic and geographic groups which may be responsible for disparities in presentation, biological behavior, treatment response and outcome.
Patients and methods: BC data from 2006-2010 at the National Oncology Center - The Royal Hospital, Oman were retrospectively retrieved from the electronic patient record system (Al-Shifa). Data were analyzed with respect to ER, PR, and Her-2 status and tumours were classified on molecular basis. Molecular subtypes were correlated with age, histology and treatment outcome. The results were compared with published regional and international data.
Results: There were 542 cases of BC accessible for evaluation. Luminal A subtype was the most common and the BCL subtype was highest among Omani females. Age was a significant factor in basal-like (63.8% younger than 50 years vs. 36.2% older than 50 years) and Her2 +ve tumours (60.9% vs. 39.1%). High grade tumors were mostly observed (41%) in basal tumors and were lowest in luminal A (19%). A higher stage at presentation (Stage III and IV) was observed in Her2+ tumours (59%), and a higher (22.4%) mortality was detected in basal like/TN tumours.
Conclusions: The molecular classification and sub-typing of BC have revealed ethnic and geographic variation. Luminal A subtype is the most common among Omani female breast cancers but it is less common than in Western females. BCL subtype is highest among Omani females compared with Western females. These differences may have diagnostic, therapeutic and prognostic implications. Large scale and multi-centre studies may confirm these findings and can be translated and incorporated to pertinent management strategies. Key Words: Molecular subtypes, breast cancer, Oman, Royal Hospital.