Abstract 285P
Background
The standard treatment for metastatic breast cancer (mBC) is systemic therapy, which has the aim to increase survival and improve the quality of life of patients (pts). Thanks to the introduction of new targeted drugs and improvements in diagnostic imaging, oligometastatic and oligoprogressive disease settings are even more common in the clinical practice. In these settings, radiotherapy (RT) could represent a valid treatment to improve disease control while maintaining the same systemic treatment. The aim of this retrospective analysis is to characterize oligoprogressive mBC pts who underwent RT without changing systemic therapy.
Methods
A retrospective analysis of mBC pts undergoing RT on up to three sites of oligoprogression with continuation of systemic therapy was conducted at Fondazione Policlinico Universitario Agostino Gemelli-IRCCS between January 2014 and December 2019. The primary endpoint was progression-free survival after RT (PFS-AR); the secondary endpoint was overall survival (OS). Subgroup Analysis (distinguish subtype, systemic therapies, site of oligoprogression) was performed. Multivariate analysis was performed on covariates with a statistical significance to predict PFS-AR and OS.
Results
On 620 mBC pts who underwent radiotherapy, 27 pts met the inclusion criteria. PFR-AR was 12.2 months (m) (95 CI 3-38 m). Exploratory subgroup analysis showed a significant association of PFS-AR with immunophenotypes (P= 0.03) and first line systemic therapy with respect to further ongoing lines of treatment (P= 0.05). Multivariate analysis conducted for PFS-AR outcomes showed an AUC of 0.832 (P= 0.92) based on immunophenotypes (p 0.004) and line of chemotherapy (P= 0.05). OS was 53 months (95% CI 16-190 m). No clinical factors were significantly associated with OS.
Conclusions
To our knowledge, this is the first study reporting a survival benefit of RT in oligoprogressive mBC, especially during first line systemic therapies and for HER2+ and luminal subtypes. These data pave the way for prospective trials to confirm the appropriate setting, timing of systemic therapies and dose of RT treatments.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
The authors.
Funding
Has not received any funding.
Disclosure
All authors have declared no conflicts of interest.