Heerfordt's Syndrome: A form of sarcoidosis that presents with a combination of parotid gland enlargement, facial palsy, uveitis, and fever. The rash associated with sarcoidosis, such as erythema nodosum, can accompany these symptoms, making Heerfordt's Syndrome a strong candidate for a diagnosis involving both a rash and a parotid tumor.

Sjögren's Syndrome: An autoimmune disorder that can cause parotid gland swelling and is often associated with skin rashes, among other symptoms like dry eyes and mouth.
Parotid Lymphoma: Lymphoma can manifest as a parotid tumor and may be associated with systemic symptoms including rashes.
Tuberculosis: Though less common, tuberculosis can cause parotid gland enlargement and may be accompanied by a rash, among other systemic symptoms.

Lymphoma (including Cutaneous T-Cell Lymphoma): Certain types of lymphoma, like mycosis fungoides, can present with skin rashes and potentially involve the parotid gland, making early diagnosis critical.
Sarcoidosis with Cutaneous Involvement: While mentioned in the most likely category, its inclusion here emphasizes the importance of not missing sarcoidosis due to its potential for serious complications if left untreated.
Parotid Metastasis from a Distant Primary Cancer: Though rare, a parotid tumor could be a metastasis from another cancer, and some cancers (like breast or lung cancer) can cause skin rashes as part of their presentation or paraneoplastic syndromes.

Kimura Disease: A rare, chronic inflammatory disorder that primarily affects the head and neck region, including the parotid gland, and can be associated with skin lesions.
IgG4-Related Disease: A condition characterized by tumor-like swelling of affected organs, including the parotid gland, and can present with skin manifestations.
Parotid Actinomycosis: A rare bacterial infection that can cause parotid gland swelling and may be associated with skin lesions or rashes.