Targeting therapy-resistant metastatic clones with SBRT in oligoprogressive breast cancer
Robbe Van den Begin,
Belgium
PO-1185
Abstract
Targeting therapy-resistant metastatic clones with SBRT in oligoprogressive breast cancer
Authors: Robbe Van den Begin1, Sarah Bellal1, Alex De Caluwé1, Philippe Aftimos2, Zelda Paquier3, Géraldine Gebhart4, Laurence Buisseret2, Philippe Martinive1, Florence Lefranc5, Dirk Van Gestel1
1Jules Bordet Institute, Radiation Oncology, Brussels, Belgium; 2Jules Bordet Institute, Medical Oncology, Brussels, Belgium; 3Jules Bordet Institute, Medical Physics, Brussels, Belgium; 4Jules Bordet Institute, Nuclear Medicine, Brussels, Belgium; 5Erasmus Hospital, Neurosurgery, Anderlecht, Belgium
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Purpose or Objective
During systemic treatment for metastatic breast cancer (mBCa), disease
progression is sometimes limited to a few resistant sites. Treating this
oligoprogression with metastasis-directed therapy such as stereotactic body
radiotherapy (SBRT) may allow to extend the benefit of the ongoing systemic
line. Given the paucity of data in mBCa, we aimed to investigate the outcomes
after SBRT for oligoprogressive disease in mBCa.
Material and Methods
Forty-one patients with mBCa treated with SBRT between 2016 and 2020 at
our department for maximum 5 extracranial oligoprogressive lesions were
included in this retrospective study. All progressive lesions must have been
treated locally and the ongoing systemic treatment had to be continued after SBRT.
Primary endpoint was next systemic treatment-free survival (NEST-FS), other
endpoints were progression-free-survival (PFS) and overall survival (OS), all measured
from start of (first) SBRT. PFS included all types of progression as an event,
also new oligoprogression amenable to new local therapy.
Results
All patients had HR+ or HER2+ disease. Eighty percent
of patients had a grade 2 or 3 invasive
ductal carcinoma and 98% of patients demonstrated 1-3 oligoprogressive lesions.
Oligoprogression occurred in bone, lymph nodes, lung or intramammary lesions. According
to the ESTRO-EORTC definitions, 12 patients (29%) had genuine oligometastatic
disease while 29 (71%) showed induced oligoprogression. Median follow-up amounted to 13,7 months. Eleven
patients (27%) received repeated local treatments for repeated oligoprogression.
Median NEST-FS was 9,2 months (95%CI: 8,0-10,4 months),
while median PFS amounted to 5,5 months (4,7-6,3). OS was estimated at 65% (44-80%)
at two years. Main significant predictors for superior NEST-FS were low disease
burden and having less than four previous lines of systemic treatment. As to
the type of treatment, best results were seen for patients receiving HER2-targeted
therapy or endocrine agents +/- CDK4/6-inhibitors.
Acute and late local grade 3
toxicity occurred in 3% and 4%, respectively, with 0% local grade 4-5 toxicity.
Conclusion
SBRT in oligoprogressive mBCa appears effective in extending the benefit
of systemic treatment, with a median additional 9,2 months before therapy is
changed. Trials are warranted to confirm these results prospectively.