The primary objective of this study is to determine the recommended dose(s) of PYX-106 in participants with relapsed/refractory solid tumors.

Inclusion Criteria:

1. Participants with histologically or cytologically confirmed solid tumors who have relapsed, been non-responsive, or have developed disease progression through standard therapy.

2. Histologically or cytologically confirmed solid tumors (see details below):

   For the dose escalation, the following solid tumors are allowed in participants who have relapsed, been non-responsive, or have developed disease progression through standard therapy and in participants for whom standard of care therapy that prolongs survival is unavailable or unsuitable (according to the Investigator and after informing the Medical Monitor): non small cell lung cancer (without driver mutations/translocations), breast cancer, endometrial cancer, thyroid cancer, kidney cancer, cholangiocarcinoma, bladder cancer, colorectal cancer, and head and neck squamous cell carcinoma.

3. Clinical sites must provide archived tissue or conduct fresh tumor biopsy (formalin-fixed paraffin-embedded [FFPE]; enough to create a minimum of 14 slides). Fresh biopsy pre-treatment is preferred, archival tissue (preferably obtained within 1 year prior to the first infusion of PYX-106) is acceptable if fresh biopsy is not medically feasible, per Investigator, at Screening. Both fresh and archival tissue samples must be collected by core needle biopsy or surgical resection. Fine needle aspirates are not permitted.

4. Eastern Cooperative Oncology Group (ECOG) Performance Status 0 or 1.

5. Participant must have at least 1 measurable lesion per Response Evaluation Criteria in Solid Tumor (RECIST) Version 1.1 criteria (by local Investigator). Participant must have radiographic evidence of disease progression per Investigator following the most recent line of treatment.

6. Life expectancy of >3 months, in the opinion of the Investigator.

Exclusion Criteria:

1. History of another malignancy except for the following: adequately treated local basal cell or squamous cell carcinoma of the skin; in situ cervical carcinoma, adequately treated; other adequately treated Stage 1 or 2 cancers currently in complete remission; any other cancer that has been in complete remission for >2 years or cancer of low risk of recurrence; or any treated or monitored indolent cancer that is unlikely to cause mortality in 5 years.
2. Known symptomatic brain metastases requiring >10 mg/day of prednisolone (or its equivalent) at the time of signing informed consent.
3. Continuance of toxicities due to prior anti-cancer agents that do not recover to Grade 1 prior to start of PYX-106 treatment, except for alopecia or endocrine deficiencies treated with stable hormone replacement therapy.
4. Presence of Grade ≥2 peripheral neuropathy.
5. Major surgery within 4 weeks prior to the start of PYX-106 treatment, as defined by the Investigator.
6. Received palliative radiation therapy within 14 days prior to the start of PYX-106 treatment.
7. Received a live vaccine within 28 days prior to the first dose of study treatment and while participating in the study.