Session Item

Stereotactic body radiotherapy (SBRT) for oligoprogressive/oligorecurrent metastases can delay next line systemic therapy. We evaluated safety and efficacy of concurrent SBRT with CDK4/6 inhibitors in stage IV breast cancer patients.

The clinical records of metastatic breast cancer patients treated with SBRT to  oligoprogressive/oligorecurrent lesions concurrently with anti-CDK4/6 inhibitors were reviewed. Toxicities were measured according to CTCAE 4.0. Response was evaluated according to RECIST/PERCIST criteria. PFS was evaluated from SBRT to local/systemic failure.

Twenty-three patients treated to a total of 50 lesions were included in the analysis. Median age was 62 years (range 38-86 years). Mean Biological Effective Dose (BED) delivered (alpha/beta=4 Gy) was 89.3 (SD = 45). SBRT was delivered to bone metastases (58%), brain metastases (16%) and visceral metastases (26%).

10 patients were treated with concurrent Palbociclib (43.5%), 9 with concurrent Ribociclib (39.1%) and 4 with concurrent Abemaciclib (17.4%).

Median FUP was 15 months (range 2-65 months). All lesions were evaluable for response: no patients experienced local failure on sites treated with SBRT. Response was evaluated on a per lesion basis. Complete response was achieved in 19 sites (38%), partial response in 17 sites (34%).

After SBRT, 1-year and 3-year PFS were 16.8% and 30.5 % respectively. Mean duration of anti-CDK4/6 therapy after SBRT was 17.6  13.9 months.  

Only two toxicities were observed: a G1 dysphagia developed in a patient treated to a cervical spine lesion and a G3 neutropenia developed in a patient treated to a central lung lesion in 8 fractions.

SBRT for oligoprogressive/oligorecurrent breast cancer metastases delivered concurrently with CDK4/6 inhibitors seems safe and effective and should be tested in prospective studies.