A Phase I Study of RGT-419B in Patients With HR-Positive, HER2-Negative Advanced Breast Cancer or Other Solid Tumors

Inclusion Criteria:

• Male or female ≥ 18 years of age

• Eastern Cooperative Oncology Group (ECOG) performance status score of 0 or 1

• Subjects with pathologically confirmed advanced solid tumors who have failedstandard-of-care therapy, or have no standard-of-care therapy available, or arecurrently not eligible for standard-of-care therapy; Subjects with HR+/ HER2-advanced or metastatic breast cancer are preferred.

• Estimated life expectancy of at least 12 weeks

Exclusion Criteria:

• Presence of visceral metastases with severe organ dysfunction

• Known active hepatitis B or C infection

• Prior irradiation to >25% of the bone marrow and/or inadequate bone marrow functionor evidence of clinicallysignificant end-organ damage

• History of allergic reactions attributed to compounds of similar chemical orbiologic composition to the drugs usedin the study