Molecular subtypes of ductal carcinoma in situ in African American and Caucasian American Women: Distribution and correlation with pathological features and outcome

Background: Molecular subtypes of breast cancer have been extensively studied in invasive carcinoma. They were shown to have a different distribution within the various ethnic populations. Few studies have applied the same classification to Ductal Carcinoma in Situ (DCIS). We report the distribution of the molecular breast cancer subtypes in DCIS between African American (AA) and Caucasian American (CA) women, their association with pathological features and outcome. Materials and methods: Tissue microarrays were constructed from paraffin blocks of 94 DCIS cases (67 AA and 27 CA) selected from a cohort of AA and CA patients diagnosed with DCIS between 1996 and 2000; mean age at diagnosis was 61 ± 12 for the AA and 58 ± 11 years for the CA group. TMA blocks were labeled with antibodies for ER, PR, HER2, Ki-67, and CK5/6. The cases were subtyped as Luminal A (ER+ and/or PR+; HER2−), Luminal B (ER+ and/or PR+; HER2+), HER2+ (ER−, PR−; HER2+), basal-like (BL) (ER−, PR−, HER2−; CK5/6+) or unclassified triple negative (UTN) (ER−, PR−, HER2−, CK5/6−). Information on grade, size and follow-up were obtained. Results: (1) Most DCIS cases were Luminal A, comprising 80% of the DCIS cases in AA and 92.6% in CA patients. (2) HER2+, BL and UTN DCIS subtypes were not seen in the CA population, and formed 9% of the DCIS cases in the AA population; these cases were all high grade. (3) In the cases with recurrence (8 AA and 1 CA patients), DCIS was Luminal A in 6 AA and 1 CA and Luminal B in 2 AA patients. Conclusion: The distribution of the molecular subtypes of DCIS did not show a significant difference between the two ethnic groups in our study. In addition, the risk of recurrence might not be higher in the non-luminal subtypes than in Luminal A and B.