This is first in human (FIH) study to a) evaluate the safety and tolerability profile of GRC54276, b) determine the maximum tolerated dose (MTD) and recommended Phase 2 doses (RP2D), and c) pharmacokinetic profile of GRC54276 alone and in combination with pembrolizumab or atezolizumab in participants with advanced solid tumors and lymphomas.

Inclusion Criteria:

1. Subjects (≥18 years of age) with histologically or cytologically confirmed advanced, metastatic, unresectable solid tumors or lymphomas who have previously received standard systemic therapy or for whom treatment is not accessible, not tolerated or refused, have progressed after ≥1 of systemic therapies for recurrent/metastatic disease and who have not received prior therapy targeting HPK1.
2. At least 1 measurable lesion as defined per RECIST 1.1. The target lesion(s) selected have not been previously treated with local therapy or the target lesion(s) selected that are within the field of prior local therapy have subsequently progressed as defined by RECIST 1.1.
3. Eastern Cooperative Oncology Group (ECOG) Performance Status ≤1 measured within 72 hours of treatment.
4. Predicted life expectancy of ≥3 months.
5. Adequate organ function as indicated by the following laboratory values up to first dose of study drug: Hemoglobin ≥9.0 g/dL, Absolute neutrophil count ≥1.5 x 109/L, Serum total bilirubin ≤1.5 x ULN (<3 x ULN for participants with Gilbert syndrome), AST and ALT ≤2.5 x ULN (≤5 x ULNs for participants with hepatocellular carcinoma or liver metastases).
6. Adequate renal function as indicated by creatinine clearance of ≥60mL/min calculated using Cokroft-Gault method.
7. Adequate cardiac function, left ventricular ejection fraction (LVEF) of ≥50% as assessed by multi-gated acquisition (MUGA) or ultrasound/echocardiography (ECHO).
8. For Part 2, dose expansion cohorts inclusion criteria specific to tumor types will be updated after completion of Part 1.

Exclusion Criteria:

1. Any condition that, in the opinion of the Investigator, would interfere with evaluation of the study drug or interpretation of subject safety or study results.

2. Subjects with uncontrolled or untreated brain metastasis or leptomeningeal disease. Subjects with equivocal findings or with confirmed brain metastases are eligible provided that they are asymptomatic and radiologically stable without the need for corticosteroid treatment for at least 4 weeks prior to the first dose of study drug(s)

3. Any active malignancy ≤2 years before the first dose of study drug(s) except for the specific cancer under investigation in this study and any locally recurring cancer that has been treated with curative intent (e.g., resected basal or squamous cell skin cancer, superficial bladder cancer, or carcinoma in situ of the cervix or breast)

4. Any condition that required systemic treatment with either corticosteroids (>10 mg daily of prednisone or equivalent) or other immunosuppressive medication ≤14 days before the first dose of study drug(s), with the following exceptions:

   1. Adrenal replacement steroid (dose ≤10 mg daily of prednisone or equivalent)
   2. Topical, ocular, intra-articular, intranasal, or inhalational corticosteroid with minimal systemic absorption
   3. Short course (≤7 days) of corticosteroid prescribed prophylactically (e.g., for contrast dye allergy) or for the treatment of a non-autoimmune condition (e.g., delayed-type hypersensitivity reaction caused by contact allergen)

5. Pregnant/planning to be pregnant or breast-feeding women.

6. Any important medical illness or abnormal laboratory finding that would increase the risk of participating in this study (based on the investigator's judgment).

7. Any known severe allergic reaction to pembrolizumab/atezolizumab or its excipients.