2753 - Characterizing Patterns of Progression on Sacituzumab Govitecan Among Patients with Triple Negative Metastatic Breast Cancer
Presenter(s)
E. S. Hollis1, D. L. Casey2, Y. Abdou3, E. L. Jones2, J. L. Wright2, G. P. Gupta2, and S. Sud4; 1University of North Carolina Hospitals, Chapel Hill, NC, 2Department of Radiation Oncology, University of North Carolina School of Medicine, Chapel Hill, NC, 3University of North Carolina at Chapel Hill, Chapel Hill, NC, 4Department of Radiation Oncology, University of North Carolina, Chapel Hill, NC
Purpose/Objective(s): Sacituzumab govitecan (SG) is an antibody-drug conjugate (ADC) approved for the treatment of metastatic triple negative breast cancer (mTNBC). Understanding disease progression patterns on this targeted therapy may identify opportunities to delay changes in systemic therapy by using metastasis-directed stereotactic body radiotherapy (SBRT) or external beam radiotherapy (EBRT) to enhance focal disease control. We aimed to quantify the frequency of progression at pre-existing sites and the proportion of patients with progression at = 5 sites, potentially amenable to SBRT/EBRT.
Materials/Methods: We retrospectively identified 40 patients evaluated at an NCI-Designated Cancer Center and affiliated satellite centers with mTNBC who received SG from 2022 to 2024. Reasons for discontinuation were abstracted from the EMR and re-staging imaging at progression was compared to imaging prior to SG initiation. Oligometastatic and oligoprogressive disease were defined as = 5 radiographically detectable lesions (total disease burden or new/progressing lesions, respectively).
Results: Among 40 patients, the median age was 54 years and the median follow-up time after starting SG was 6.6 months. SG was given as the median 2nd line of systemic therapy for mTNBC, with patients receiving a median of 5 cycles (range: 1-25). Reasons for SG discontinuation included disease progression (28/40, 70%), toxicity (1/40, 2.5%), death or hospice transition (11/40, 27.5%). At initial presentation, 15/40 (37.5%) patients had oligometastatic disease and 11/40 (27.5%) remained oligometastatic at the start of SG. Intracranial metastases were seen in 4/40 (10%) patients at diagnosis. Imaging was available in 35/40 cases of progression to determine sites and patterns of progression. Progression occurred at pre-existing sites (present at or before SG initiation) in 33/35 patients (94%), with 8/35 (22.9%) involving pre-existing sites only and 25/35 (71.4%) involving both pre-existing and new sites. Progression at new sites only was observed in 2/35 patients (5.7%). Oligoprogression was seen in 12/35 (34.2%) patients, half of which (6/12, 50%) had progressive sites amenable to SBRT while all (12/12 (100%)) had sites amenable to a combination of SBRT or EBRT. Despite this, only 5 patients underwent RT during SG treatment, with 12 patients undergoing RT after SG discontinuation. Intracranial progression occurred in 9/35 (26%) patients. Additionally, 24/40 (16%) patients went on additional lines of therapy, with a median of 1 additional line of therapy.
Conclusion: First progression in patients with mTNBC on SG was oligoprogressive and amenable to SBRT and/or EBRT in ~1/3 of patients. Most (33/35, 94%) progression events involved pre-existing metastatic sites. These findings support further exploration of RT as a consolidation and/or salvage strategy to enhance time on ADC therapy and possibly disease control in patients receiving SG.