A Study to Evaluate INCB099280 in Participants With Advanced Cutaneous Squamous Cell Carcinoma

Inclusion Criteria:

• Histopathological diagnosis of cSCC.

• Previously untreated or recurrent locally advanced (without nodal metastases) ormetastatic (distant or regional metastasis) cSCC not amenable to curative surgeryand/or radiotherapy.

• Measurable disease based on either radiographic imaging per RECIST 1.1 or WHOcriteria.

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

• Life expectancy > 3 months.

• Willingness to avoid pregnancy or fathering children.

Exclusion Criteria:

• Known history of an additional malignancy.

• Central nervous system (CNS) metastases requiring treatment and/or leptomeningealdisease.

• Toxicity from prior therapy that has not recovered.

• Prior receipt of an anti-PD-1, anti-PD-L1, or anti-PD-L2 agent; treatment with animmune modulator (eg, CTLA-4, GITR, LAG3, TIM3, OX40, ICOS, IL-2, 4-1BB, CAR-Tcell).

• Received thoracic radiation within 6 months of the first dose of study treatment.

• Participation in another interventional clinical study while receiving INCB099280.

• Impaired cardiac function or clinically significant cardiac disease.

• History or evidence of interstitial lung disease including noninfectiouspneumonitis.

• Presence of gastrointestinal conditions that may affect drug absorption.

• Any autoimmune disease requiring systemic treatment in the past 5 years.

• Diagnosis of primary immunodeficiency or receiving chronic systemic steroid therapyat a daily dose exceeding 10 mg of prednisone or equivalent.

• Active infection requiring systemic therapy.

• History of organ transplantation, including allogeneic stem cell transplantation.

• Receipt of systemic antibiotics within 28 days of first dose of study treatment.

• Probiotic usage is prohibited during screening and throughout the study treatmentperiod.

• Received a live vaccine within 28 days of the planned start of study drug.

• Laboratory values outside the Protocol-defined ranges.

• Inadequate organ function.

Other protocol-defined Inclusion/Exclusion Criteria may apply.