Phase II Study of REPotrectinib With or Without Fulvestrant in Patients With Hormone Receptor-positive Human Epidermal Growth Factor 2-negative Metastatic Invasive LObular Carcinoma Who Received a Prior Endocrine Therapy in Combination With Cyclin-dependent Kinase 4 and 6 Inhibitor (REPLOT Trial)

Conditions

To find out if the combination of repotrectinib and fulvestrant can control the disease in participants with metastatic invasive lobular carcinoma.

Experimental: Cohort 1
Cohort 1 will include participants who have never received fulvestrant before. The first 15 participants enrolled in Cohort 1 will receive the study drug combination starting on Day 1 of their first treatment cycle. The next 14 participants enrolled in Cohort 1 will begin with fulvestrant alone for at least 12 days and then start repotrectinib sometime between Days 13 and 20 (depending on when their Cycle 1 biopsy is performed). This is done in order to use the biopsy results to study the effects of fulvestrant alone in these patients.
Experimental: Cohort 2
About 6 months after the first 15 participants are enrolled, based on their study data, Cohort 2 will begin enrolling up to 29 participants who have received fulvestrant in earlier treatments. Participants in Cohort 2 will receive repotrectinib alone.

Safety and adverse events (AEs) [ Time Frame: Through study completion; an average of 1 year ]

Facility	City	State	ZIP	Site coordinators
MD Anderson Cancer Center	Houston	Texas	77030	-

By research site