ESTRO 2024 - Abstract Book

S1925

Clinical - Mixed sites, palliation

ESTRO 2024

1 University College Cork, Cancer Research @UCC, Cork, Ireland. 2 Cork University Hospital, Department of Radiation Oncology, Cork, Ireland. 3 Princess Margaret Cancer Centre, University Health Network, Radiation Medicine Program, Toronto, Canada. 4 University of Toronto, Department of Radiation Oncology, Toronto, Canada. 5 Princess Margaret Cancer Centre, Radiation Medicine Program, Toronto, Canada. 6 Princess Margaret Cancer Centre, Department of Biostatistics, Toronto, Canada. 7 Princess Margaret Cancer Centre, Division of Medical Oncology and Hematology, Toronto, Canada. 8 Princess Margaret Cancer Centre, University Health Network, Division of Medical Oncology and Hematology, Toronto, Canada. 9 Princess Margaret Cancer Centre, University Health Network, Department of Medical Physics, Toronto, Canada. 10 Princess Margaret Cancer Centre, University Health Network, Department of Medical Imaging, Toronto, Canada. 11 Western University, London Regional Cancer Program, Division of Radiation Oncology, London, Canada

Purpose/Objective:

Oligoprogressive (OP) metastatic disease is a state whereby there are a limited number of metastatic areas progressing (often ≤5) on a background of widespread metastatic disease. While the current standard of care for OP disease is a change in systemic therapy, the use of radiotherapy (RT), and more specifically stereotactic body radiotherapy (SBRT), is being explored as a potential alternative and/or additional management option in delaying further disease progression.

Material/Methods:

A single-centre phase 2 prospective research ethics board-approved study enrolled patients with metastatic genitourinary (GU), breast and gastrointestinal (GI) cancers, receiving ST for at least 3 months, with radiographic evidence of OP disease in up to 5 sites. Patients enrolled received SBRT to all sites of OP disease in 1-5 fractions, based on standard-of-care dose-fractionation schedules at our institution for the site being treated, and were maintained on their current line of systemic therapy. We present the primary endpoint of efficacy and secondary oncologic endpoints including cumulative incidences of local control, distant failure (at a non-irradiated distant site), change in systemic therapy after SBRT using the Aalen Johansen method, where mortality without events of interest was treated as a competing event. Overall survival was estimated using Kaplan-Meier method and compared between diagnosis groups using log-rank test. Univariate and multivariable Cox proportional hazard and Fine-Gray competing risk models were performed. A two-sided p-value of <0.05 was considered as statistical significance.

Results:

Overall, 71 patients were enrolled between Oct 2019-Feb 2023, with primary tumor sites of GU (32 patients; 45%), breast (23 patients; 32%), GI (15 patients; 21%) and melanoma (1 patient; 1%) cancers (Table 1). Median age was 69 years (Interquartile range [IQR] 57-74), 32 patients (45%) were female, and median number of lines of systemic therapy at time of enrolment was 3 (IQR 2-3).

Enrolment on study was at a median of 5 years (interquartile range (IQR) 2.2-10) from initial cancer diagnosis and demonstrated 1 (80%), 2 (11%), 3 (3%), and 4 (6%) sites of OP metastases, most commonly in the liver (26 patients;