Clinical outcomes of solid basaloid and classic adenoid cystic carcinoma of the breast.

Abstract

e12746 Background: Adenoid cystic carcinoma (AdCC) of the breast is a rare ( < 0.1%) form of breast cancer with two variants, solid basaloid (SB-AdCC) and classic (C-AdCC). Due to its rarity, limited outcome data exists. We aimed to describe clinicopathological features and long-term outcomes in patients with SB-AdCC and C-AdCC. Methods: Patients diagnosed with stage I-III AdCC between 2007-2024 were retrospectively identified from an institutional database. Patient characteristics were compared between groups using Fisher’s exact test and Wilcoxon rank sum test. Recurrence free survival (RFS) was estimated using the Kaplan-Meier method and compared between groups using log-rank test. Results: 77 patients were included. The median age was 58 (IQR 48,69). Most patients self-identified as White (n = 64, 86%) and not Hispanic (n = 65, 89%). Most patients (n = 55, 71%) had SB-AdCC histology and 22 patients (29%) had C-AdCC. Median tumor size was 17 mm (IQR 13,26), with no significant size difference between SB-AdCC and C-AdCC (p = 0.5). Most patients (n =44, 57%) presented with clinical stage I disease and 34 (50%) patients had grade 3 disease, with a higher proportion of high-grade disease in patients with solid basaloid subtype (p < 0.001). Eight patients (10%) were clinically node-positive at presentation. Nearly all tumors were ER-/HER2- (88%, n = 68). Most patients underwent breast conserving therapy (70%, n = 52). Forty percent (n = 31) of patients received systemic treatment. Patients with Sb-AdCC were more likely to receive systemic therapy, 53% vs 9% (p<0.001). Among patients who received systemic therapy (n = 31), the majority (n = 19, 61%) received anthracycline–based chemotherapy, 9 (29%) received taxane-based therapy, and 3 (10%) received CMF. Few patients overall (n = 10, 13%) received immunotherapy. All patients who received neoadjuvant systemic therapy (n = 10, 14%) had Sb-AdCC histology, and none achieved pCR. Overall, 67% (n = 47) of patients received radiation, 42 (89%) after lumpectomy and 5 (11%) after mastectomy. Median RFS was 7.2 years; 18 years for C-AdCC and 5.6 years for Sb-AdCC (p = 0.014). There was no significant difference in median RFS by receipt of systemic therapy in patients with Sb-AdCC (p = 0.8). Conclusions: Despite the use of standard systemic therapy, patients with Sb-AdCC have much worse oncological outcomes compared to C-AdCC. Alternative systemic therapy options are urgently needed. Patient age and disease-related factors by AdCC variant. Overall N=771 1 Classic AdCC N=221 1 Solid Basaloid AdCC N=551 1 p-value 2 Age 58 (48,69) 60 (50,70) 56 (48,68) 0.4 Subtype ER-/HER2- 68 (88%) 17 (77%) 51 (93%) 0.11 ER+/HER2- 9 (12%) 5 (23%) 4 (7.3%) Tumor Size (mm) 17 (13, 26) 18 (14, 26) 16 (11, 25) 0.5 Grade 1 6 (8.8%) 5 (26%) 1 (2.0%) <0.001 2 28 (41%) 13 (68%) 15 (31%) 3 34 (50%) 1 (5.3) 33 (67%) 1 Median (IQR); n (%). 2 Wilcoxon rank sum test; Fisher’s exact test.