Introduction: breast cancer is among the most common cancers among women in most of Africa. However, features of histologically confirmed breast cancers presenting in specific regional populations is limited. Our study describes the clinic-pathologic features of invasive breast cancer diagnosed in women undergoing biopsy for a clinically apparent mass in Senegal, West Africa.

Methods: a prospective cohort of 522 Senegalese women presenting consecutively to Dantec Hospital (University of Dakar Tumor Institute) with a breast mass were included in the study cohort. Demographic data was collected by survey and 197 (37.7%) core needle biopsy-confirmed invasive breast cancers available for review were subsequently centrally reviewed at the University of Washington in Seattle to further to characterize the pathologic features and to perform immunohistochemistry for ER/PR and HER2.

Results: seventy six (76.1%) of the 522 Senegalese women presenting for biopsy of a clinically apparent breast mass were diagnosed with invasive breast cancer. The average age of a woman with invasive cancer was 46 years old, and most (83%) presented with Stage III or IV disease. The predominant histologic subtype among the 197 biopsy-confirmed cancers was invasive ductal carcinoma (98%), with few cases of invasive lobular carcinoma (2%). Cancers were classified into four clinically relevant treatment IHC groups by combined ER/PR status and HER2 status as follows: ER-/PR-, HER2- (n=92; 46.7%), ER-/PR-, HER2+ (n=20; 10.1%), ER+/PR+, HER2- (n=76; 38.6%) and ER+/PR+, HER2+ (n=9; 4.6%). Age at time of diagnosis was similar between these four subgroups although more HER2 positive cases were pre-menopausal (p=0.05). Stage of disease at presentation differed by IHC group (p=0.008), with HER2+ cancers significantly more likely to present with stage IV disease than other IHC groups, including ER-/PR-, HER2-. There were no significant differences between groups by age group, ethnicity, place of residence or birth, or parity.

Conclusion: our analysis of breast cancer cases in Senegal shows a distribution of clinically relevant IHC groups like that seen in the few prior studies of breast cancer in West Africa, with higher frequencies of triple negative cancers than in most United States and European populations. Mean age at presentation, delayed presentation, and genetic/regional risk factors likely influence these differences. A better understanding of the frequencies of the pathologic features of breast cancers in the West African population may help guide future genetic studies as well as appropriate clinical management of breast cancer in these populations.