This phase I/II trial tests the safety and efficacy of split-course adaptive radiation therapy in combination with immunotherapy with or without chemotherapy for the treatment of patients with stage IV lung cancer or lung cancer that that has spread to nearby tissue or lymph nodes (locally advanced). Radiation therapy is a standard cancer treatment that uses high energy rays to kill cancer cells and shrink tumors. Split-course adaptive radiation therapy uses patient disease response to alter the intensity of the radiation therapy. Immunotherapy with monoclonal antibodies such as pembrolizumab, ipilimumab, cemiplimab, atezolizumab or nivolumab may help the body's immune system attack the cancer, and may interfere with the ability of tumor cells to grow and spread. Chemotherapy drugs like carboplatin, pemetrexed, and paclitaxel work in different ways to stop the growth of cancer cells, either by killing the cells, by stopping them from dividing, or by stopping them from spreading. Giving split-course adaptive radiation therapy with standard treatments like immunotherapy and chemotherapy may be more effective at treating stage IV or locally advanced lung cancer than giving them alone.

This is a multi-center, first-in-human (FIH), open-label, Phase 1a/1b dose escalation and dose expansion study to assess the safety, PK, pharmacodynamics, and antitumor activity of PHST001 monotherapy (Phase 1a) or in combination with anticancer therapies (Phase 1b) in adult participants with advanced relapsed and/or refractory solid tumors (including but not limited to CNS tumors in Phase 1a only). Phase 1b will include the following cohorts 1) tumor-specific cohorts for participants with advanced relapsed and/or refractory ovarian cancer, endometrial cancer, and cholangiocarcinoma, 2) a randomized cohort for participants with ovarian cancer who will receive PHST001 in combination with mirvetuximab soravtansine, 3) a cohort for participants with advanced/metastatic breast cancer who will receive PHST001 in combination with trastuzumab deruxtecan and 4) a cohort of patients who consent to additional biomarker studies.

The study's primary objectives are to evaluate the safety and tolerability of PHST001 and determine the RP2D (Recommended Phase 2 dose) of PHST001 as monotherapy and in combination with anticancer therapies, as well as to assess the anti-tumor activity of PHST001 in combination with anticancer therapies in Phase 1b.