Molecular subtypes of breast carcinoma in Saudi Arabia. A retrospective study

To determine the distribution of various molecular subtypes of breast cancer in Saudi Arabia and to assess the association between these subtypes and age at diagnosis, tumor size, histopathological type, grade, presence of carcinoma in-situ, and lymph node status.

This observational retrospective study, between January 2010 and  December 2014, was conducted at King Khalid University Hospital, Riyadh, Saudi Arabia. We classified 359 breast cancers into 4 molecular subtypes, using immunohistochemistry: luminal A (estrogen receptor [ER], or progesterone receptor [PR] positive and human epidermal growth factor receptor 2 [HER2] negative), luminal B (ER and/or PR positive and HER2 positive), HER2-positive (ER and PR negative and HER2 positive), and triple negative (ER, PR, and HER2 negative). We evaluated the relationship between these subtypes and clinicopathological features using Chi square test.

The most prevalent subtype was luminal A (58.5%), followed in descending order of frequency by triple negative (14.8%), luminal B (14.5%), and HER2-positive (12.3%). The average age at diagnosis was 49.8 years, and average tumor size at diagnosis was 3.19 cm.

Luminal A tumor was the most common molecular subtype and HER2-positive was the least common. Most lobular carcinomas were luminal A tumors. Human epidermal growth factor receptor 2-positive and triple negative tumors had a higher histologic grade and a larger tumor size at diagnosis, and they were more common in women under 50 years. Carcinoma-in-situ was least common in triple negative tumors. We found no association between lymph node status and molecular subtypes.