The subject can participate in this study if the subject:

1. Has a tumor with a confirmed MTAP loss
2. Is equal or greater than 18 years of age at the time of signature of the main study ICF
3. Has had progression or an inadequate response to or is intolerant of the approved standard of care therapy, no standard of care therapy exists, or the investigator has determined that treatment with the standard of care therapy is not appropriate.
4. Is able to swallow tablets
5. Has adequate organ function/reserve per local labs
6. Negative serum pregnancy test result at screening
7. Has an ECOG performance status score of 0 to 1
8. Has measurable disease based on RECIST v1.1 or a confirmed glioblastoma (IDH-wildtype) with radiographic evidence of disease progression or recurrence defined by RANO 2.0.
9. Has an ECOG performance score of 0 to 1 or for GBM has a Karnofsky performance status score equal or greater than 70.

The subject cannot participate in this study if the subject:

1. is a female patient is who is pregnant or breastfeeding
2. Has impaired GI function or disease that may significantly alter the absorption of oral study treatment(s)
3. Has an active infection requiring systemic therapy
4. Has received prior treatment with a PRMT5 inhibitor or a MAT2A inhibitor
5. Patients in the expansion receiving the combination therapy that have received prior treatment with a CDK4/6 inhibitor
6. Clinically relevant cardiovascular disease
7. Has a prior or ongoing clinically significant illness may affect the safety of the patient, impair the assessment of study results or compliance with the protocol