Abstract P3-08-26: Clinico-pathological characteristics of metaplastic breast cancer as compared to normal TNBC: A single center analysis
Authors: Ardui Jan , Punie Kevin , Floris Giuseppe , Izci Hava , Wildiers Hans , Vergote Ignace , Berteloot Patrick , Van Gorp Toon , Laenen Annouschka , Smeets Ann , Weltens Caroline , Neven Patrick 
Published: March 2020

Abstract
Purpose: Metaplastic Breast Cancer (mBC) is uncommon and often behaves aggressive with a high incidence of recurrence. Prognostic factors are poorly understood. We analyzed prognostic factors in a single center series of triple negative mBC and compared those to a patients with ductal TNBC of no special type (dTNBC-NST), treated during the same time period;
Materials and methods: We retrospectively analyzed prognostic factors (demographic and clinical pathological features) and distant recurrence of all ER-negative mBC’s (primary operated and neoadjuvant chemotherapy (NAC-)) treated in the University Hospitals Leuven (UHL) between 1/1/2000 and 31/12/2016. TNBC was defined as IHC-ER&lt;1%, IHC-PR&lt;1% and IHC-HER2 0-1+ and FISH negative if HER2 IHC 2/3+. For comparison, only ductal TNBC of no special type were included (dTNBC-NST). Demographic features included age, Body Mass Index (BMI, kg/m²) and detection method. Clinical pathological features included grading, size, lymphovascular invasion (LVI) and nodal involvement. Outcome included distant recurrence rate. The Cox proportional hazards model was used to analyze prognostic factors on distant recurrence rate. A multivariate model was used to correct for possible confounders (grade, nodal stage, tumor size). The clinical pathological variables were compared using Fisher exact test or Mann-Withney U test. All tests are two-sided and a 5% significance level is assumed for all tests. Results on distant recurrent rates are presented as hazard ratios (HR) with 95% confidence intervals (CI).
Results: 49 mBC patients were identified; 11 treated with NAC and 38 primary operated. The dTNBC-NST group contained 662 patients; 194 treated with NAC and 468 primary operated. Median follow up was 8.35yrs [5.33 - 12.16] in the mBC and 9.48yrs [5.23-13.44] in the dTNBC-NST group. Median age was 52yr in the mBC and 53yr in the dTNBC-NST (p=0.482). There was a tendency for a higher BMI in the mBC group: median BMI was 26.4kg/m² in mBC and 24.7kg/m² in the dTNBC-NST group (p=0.09, univariate analysis). Tumors were significantly larger in the mBC group with the median size (mm) of 29.5 in mBC and 25.0 in dTNBC-NST (p=0.008). Nodal involvement was 17/49 (34.7%) in the mBC group and 205/662 (31.0%) in dTNBC-NST (p=0.345). LVI was significantly less present in mBC (7.9%) than in dTNBC-NST (24.4%) (p=0.026). A similar proportion in either group received adjuvant chemotherapy (76.3% in mBC and 80.8% in dTNBC-NST) but mBC received more often adjuvant radiotherapy (85.7% in mBC and 60.1% in dTNBC-NST, p&lt;0.01) despite having a similar mastectomy rate (51.0% in mBC and 47.6% in dTNBC-NST, p=0.659). pCR in NAC treated mBC was achieved in 4/11 (36.4%) and in 86/194 (43.9%) of dTNBC-NST (p=0.785). There is a tendency to a higher distant relapse rate in mBC with 28.9% (95% CI: 16.5;42.5) having distant relapse within 5 years compared to 16.6% (95% CI: 13.8;19.7) in dTNBC-NST) [HR 1.722, 95% CI (0.970 - 3.057), p=0.064)]. However, when corrected in a multivariate model (corrected for grade, nodal stage and size) this trend becomes irrelevant [HR 1.189, 95% CI (0.659 - 2.144)].
Conclusion: mBC is larger at diagnosis and less often LVI-pos compared to dTNBC-NST. Adjuvant radiotherapy was more often given to mBC patients. The trend we observed of more distant relapse in mBC disappeared when corrected for tumor characteristics.
Citation Format: Jan Ardui, Kevin Punie, Giuseppe Floris, Hava Izci, Hans Wildiers, Ignace Vergote, Patrick Berteloot, Toon Van Gorp, Annouschka Laenen, Ann Smeets, Caroline Weltens, Patrick Neven. Clinico-pathological characteristics of metaplastic breast cancer as compared to normal TNBC: A single center analysis [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-08-26.