Academy of Medical Sciences of I.R. Iran Archives of Iranian Medicine 1029-2977 24 11 2021 11 01 Comparison of Different Molecular Subtypes with 14% Ki-67 Cut-off Threshold in Breast Cancer Patients of Pakistan- An Indication of Poor Prognosis 837 844 10.34172/aim.2021.124 EN Mehreen Mushtaq Summaya Sohail Chaudry https://orcid.org/0000-0003-1395-6960 Ahmareen Khalid Sheikh Nazia Khan Asma Khattak Aisha Akbar Ashok Kumar Tanwani Tanwir Khaliq Muhammad Faraz Arshad Malik Syeda Kiran Riaz https://orcid.org/0000-0001-7965-4178 Journal Article 10.34172/aim.2021.124 2020 10 08 2020 12 15 Background: Ki-67 is a proliferation marker that is used not only to categorize patients in luminal A and B subtypes of breast cancers, but also to determine the aggressiveness of the disease in triple negative and human epidermal growth factor 2 (HER2) over expressed molecular subtypes. The present study was designed to evaluate the role of Ki-67 with cut off value of 14% in molecular subgroups and its association with patient prognosis. Methods: Immunostaining was performed on histopathologically confirmed sections (n = 278) to assess expression of Ki-67, estrogen receptor (ER), progesterone receptor (PR) and HER2. Immunoreactivity of molecules was recorded as percentage scoring. Results: Adopting a cut off value of 14%, Ki-67 was high in 88%of the cases included in the study. High Ki-67 was significantly associated with pathological parameters including histological grade, advanced stage and nodal/distant metastasis. Immunoexpression of ER, PR and HER2 also showed strong correlation with high expression of Ki-67. Based on the St. Gallen classification, the cases were categorized into luminal A (10%) and luminal B (51%), triple negative (20%) and HER2 enriched (18%). Ki-67 index was also significantly high in 98% of HER2 enriched and 95% of TNBC patients. Interestingly, Ki-67 score with cut off value of 14% proved to be significant in deciphering prognosis in luminal patients. Moreover, high expression of Ki-67 also proved to be a marker of poor prognosis, especially in triple negative patients. Conclusion: We suggest that utilization of IHC4 status i.e. ER, PR, HER2 and Ki-67 along with pathological findings and molecular subtyping can considerably affect clinical as well as therapeutic decisions.