Abstract P3-08-31: Clinical and pathological features of invasive micropapillary carcinoma of the breast and correlation with prognosis
Authors: Punie Kevin , Deman Frederik , Laenen Annouschka , Faes Timothy , Wildiers Hans , Smeets Ann , Nevelsteen Ines , Van Ongeval Chantal , Baten Adinda , Christiaens Melissa , Oldenburger Eva , Janssen Hilde , Weltens Caroline , Geukens Tatjana , Willers Nynke , Ardui Jan , Izci Hava , Slembrouck Laurence , Neven Patrick , Desmedt Christine , Floris Giuseppe 
Published: March 2020

Background and objective: Invasive micropapillary carcinoma (IMPC) of the breast is a special variant of breast carcinoma with a unique morphology. Data about long-term outcome are conflicting and reports on stromal tumor infiltrating lymphocytes (sTILs) and their correlation with prognosis are scarce. In this retrospective cohort study we aimed to describe clinical and pathological features of IMPC, including sTILs assessment and immunohistochemistry studies, and their correlation with long-term outcome. Materials and methods: Patients with stage I-III IMPC (pure and mixed forms) who underwent upfront surgery at our institution between 2000 and 2016 were included. All patients signed informed consent. Standard clinico-pathological features and follow-up data to calculate distant relapse-free interval and breast cancer-specific survival were obtained from clinical records. Pathologic review of representative H&E-slides of the resection specimens included evaluation of sTILs and assessment of the micropapillary component. Surrogate molecular subtypes were based on receptor-status and histological grade. Using tissue microarrays we assessed by immunohistochemistry the pattern of staining of P53, and scored semi-qualitatively the expression of Bcl2, PAX8 and WT1. The association between predictors and outcome is analyzed using the Fine and Gray model, accounting for other-cause death as competing event. All tests are two-sided, assuming a 5% significance level. The sample size did not allow multivariate analysis. Results: We included 111 patients (median age 61,5 years; range 33-88). Luminal surrogate subtypes were most prevalent with 51 luminal A-like, 41 luminal B-like, 12 luminal HER2+, 5 HER2+ and 2 triple negative IMPC. 89% of patients had a T1 or T2 tumor and 50% of IMPC were poorly differentiated. Lymph node involvement was present in 59% and lymphovascular invasion in 44% of cases. Adjuvant chemotherapy, radiotherapy and endocrine therapy was administered in 47%, 87% and 90% of patients, respectively. Of all cases 59% were pure IMPC. Standard clinico-pathological features were comparable between pure and non-pure IMPC. sTILs were classified as low (&lt;30%), intermediate (30-50%) and high (&gt;50%) in 78%, 14% and 8% of specimens respectively. Comparison between surrogate subtypes showed higher sTILs (p=0.025) and a higher likelihood of aberrant P53 expression (p&lt;0.001) in HER2+ compared to luminal A-like subtype. Immunohistochemistry studies performed on 105 samples with enough material showed aberrant P53 expression in 10% and WT1 nuclear expression in 7% of cases. Pax8-staining was negative in all IMPC in this cohort. Bcl-2 expression was strongly related to all luminal subtypes (p&lt;0.03). After a median follow-up of 100 months, we observed 8 distant relapses (7,2%) and 3 breast cancer-related deaths (2,7%). All events occurred in non-pure IMPC. Surrogate subtypes for patients with distant relapses where luminal A-like in 4 patients while the other subtypes where each observed in 1 patient. Five out of eight patients with distant relapse had received prior adjuvant chemotherapy. Six had lymph node involvement. Higher median sTILs was correlated with worse distant relapse-free interval (HR=1.55; p=0.0172) and breast cancer-specific survival (HR=2.10; p&lt;0.001). Conclusions: Standard clinico-pathological features were similar in pure and non-pure IMPC. Despite high proportion of grade 3 differentiation and lymph node involvement, we observed a low rate of distant metastasis and within the pure IMPC (59% of patients), no distant relapses occurred. These findings could be explained by the high proportion of luminal-A like tumors in our cohort and need confirmation. Higher sTILs was associated with worse outcome in this IMPC cohort, confirming previously published observations.

Citation Format: Kevin Punie, Frederik Deman, Annouschka Laenen, Timothy Faes, Hans Wildiers, Ann Smeets, Ines Nevelsteen, Chantal Van Ongeval, Adinda Baten, Melissa Christiaens, Eva Oldenburger, Hilde Janssen, Caroline Weltens, Tatjana Geukens, Nynke Willers, Jan Ardui, Hava Izci, Laurence Slembrouck, Patrick Neven, Christine Desmedt, Giuseppe Floris. Clinical and pathological features of invasive micropapillary carcinoma of the breast and correlation with prognosis [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 P3-08-31.