Differential Clinical Outcomes of Palliative Radiotherapy among Different Molecular Subtypes of Metastatic Breast Cancer: A Prospective Study

Thimmaiah, Naveen; Naveen, Nirupama; Saini, Ayushee; Krishna, Uday; Kannan, Mageshraja; Pasha, Tanvir; Poojar, Sridhar

doi:10.31557/APJCP.2026.27.3.1029

Differential Clinical Outcomes of Palliative Radiotherapy among Different Molecular Subtypes of Metastatic Breast Cancer: A Prospective Study

Document Type : Research Articles

Authors

¹ Department of Radiation Oncology, Kidwai Memorial Institute of Oncology, Bangalore, India.

² Department of Gynaecological Oncology, Kidwai Memorial Institute of Oncology, Bangalore, India.

³ Department of Radiation Oncology. Medanta Hospital, India.

⁴ Department of Radiation Oncology, Apollo Proton Centre, Chennai, India.

⁵ Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bangalore, India.

10.31557/APJCP.2026.27.3.1029

Abstract

Background: Molecular classification is used to tailor systemic therapy in breast cancer (BC). However, there is a paucity of literature correlating the response to radiotherapy with molecular subtypes of metastatic breast cancer (MBC) This prospective study intends to evaluate the differences in clinical outcomes in the different molecular subtypes of MBC to hypofractionated palliative radiotherapy (HPRT). Methods: MBC patients between December 2021 to September 2022, with Karnofsky Performance status > 70, were enrolled and treated with HPRT. All patients received systemic therapy. All patients were evaluated until 12 months post-radiotherapy. The molecular subtype of BC, local control (LC), and progression-free survival (PFS) were documented. Result: Eighty patients were recruited, with a mean age of 51 ± 10.48 years. Twelve of 80 patients expired, and 16 of 80 patients were lost to follow-up. The molecular subtypes were: Luminal B (37.5%), Luminal A (30%), TNBC (20%) and HER2+ (12.5%). At 6 months post-RT, 61.5% patients had local control (LC) at their metastatic site, whereas 38.5% had Progressive disease (PD). At 12 months, 71.1% had LC at the metastatic site, and 28.9% had progression. Local control at 6 months by subtype: Luminal A - 83%, Luminal B - 60%, HER2+ – 50% and TNBC – 31.2% (p = 0.01). The median progression-free survival (PFS) of the study group was 6 months (95% CI: 4.78-7.22), with TNBC patients performing the poorest. Conclusion: Luminal subtypes have better local control and progression-free survival post-HPRT compared to TNBC and HER2+ subtypes, which can further be used to stratify radiotherapy fractionation schedules.

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