• Fugen Vardar Aker, Erhan Ekren, Meryem Dogan, Gunay Gurleyik, Eda Tanrikulu, and Basak Bala Oven.
• Department of Pathology, University of Health Sciences, Haydarpasa Numune Training and Research Hospital, Istanbul, Turkey.
• J Coll Physicians Surg Pak. 2022 Sep 1; 32 (9): 1196-1201.

ObjectiveTo evaluate whether there are differences in invasive micropapillary carcinoma (IMPC) and invasive ductal carcinoma-NOS (IDC-NOS) according to the clinicopathological features and prognosis including molecular subtypes.Study DesignDescriptive study.Place And Duration Of StudyDepartment of Pathology, University of Health Sciences, Haydarpasa Numune Training and Research Hospital, Istanbul, Turkey, from 2003 to 2016.MethodologyOperated breast cancer cases (58 IMPC + 326 IDC-NOS), with long-term follow-up findings (cases followed up until 2020), were reviewed. The cases, whose other component was only IDC-NOS, were included in the mixed IMPC group. The clinical features, including clinical presentation, treatments, and follow-up information were obtained from the patient clinical database. The IMPC cases included in the study were re-examined, and micropapillary tumour components were confirmed based on the criteria set by the World Health Organisation (WHO). The clinicopathological findings, recurrence, and survival data of both groups were compared. In addition, IDC-NOS was divided into the molecular subgroups and compared with IMPC cases in terms of 5-year overall survival (OS).ResultsThere was no significant difference between the two groups for the distribution of molecular subtypes. There was a statistically significant difference among the nuclear grade, tumour size, nodal status, lymphovascular, and perineural invasion. In the first 5-year period, the OS rate for IDC-NOS and IMPC was 90.8% and 86.2% (p<0.05). The 5-year OS rate of luminal A, luminal B, HER2, triple negative (TN), and IMPC patients was 97.6%, 91.3%, 90%, 70%, and 86.2%, respectively (p<0.05). The OS rate in patients with TN and IMPC was similar which was found significantly lower than the other groups (luminal A, luminal B, and HER2). The median OS was 51.3 months and 53.9 months for the patients with TN and IMPC, respectively (p<0.001). This difference disappeared in the 10th and 15th years of follow-up.ConclusionThe majority of the deaths in IMPC occurred within the first 5 years. The 5-year OS rates were similar in the TN and IMPC patients. The survival pattern of IMPC is parallel with TN, Therefore, clinical, therapeutic, and prognostic evaluation in IMPC can be done like TN.Key WordsInvasive ductal carcinoma, Invasive micropapillary carcinoma, Survival.

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