Melasma: This is a common condition characterized by patches of brown or gray skin, typically on the face, and is often associated with hormonal changes or sun exposure.

Solar Lentigines (Liver Spots): These are benign spots that appear as a result of sun exposure, and they can resemble brown marks on the cheek.
Post-Inflammatory Hyperpigmentation (PIH): This condition occurs after inflammation or injury to the skin, leading to brown marks or discoloration.
Cafe-au-Lait Macules: These are benign spots or patches that range in color from light brown to chocolate brown and can appear anywhere on the body, including the cheek.

Malignant Melanoma: Although less likely, it is crucial to consider melanoma, especially if the brown mark is asymmetric, has irregular borders, color variation, diameter larger than 6mm, or is evolving.
Dermatofibroma: A benign growth that can appear as a brown mark, but it's essential to rule out more serious conditions.

Naevus of Ota: A rare condition characterized by hyperpigmentation, typically on one side of the face, including the cheek, due to melanin deposition in the dermis.
Ephelides (Freckles): While common, when appearing in unusual patterns or numbers, they might be considered under rare diagnoses, especially if associated with other systemic conditions.
Pigmented Basal Cell Carcinoma: A rare form of skin cancer that can present as a brown mark, emphasizing the importance of thorough examination and possibly biopsy for definitive diagnosis.