Basal Cell Carcinoma: This is a common skin cancer that can present as a rapidly growing nodule, especially in sun-exposed areas. It is often pigmented and can ulcerate.

Squamous Cell Carcinoma: Another form of skin cancer that can grow rapidly, often appearing as a firm, red nodule. It is more aggressive than basal cell carcinoma and can metastasize.
Keratoacanthoma: A low-grade, rapidly growing tumor that resembles squamous cell carcinoma but often has a more benign course and can regress spontaneously.
Pyogenic Granuloma: A benign vascular tumor that can grow rapidly, typically appearing as a red, bleeding nodule, often in response to trauma.

Merkel Cell Carcinoma: A rare, aggressive skin cancer that can present as a rapidly growing, firm, flesh-colored nodule. It has a high risk of metastasis and requires prompt treatment.
Melanoma: Although less common, melanoma can grow rapidly and must be considered in the differential diagnosis of any new or changing skin nodule, especially if it exhibits the ABCDE criteria (asymmetry, border irregularity, color variation, diameter >6mm, evolving).
Cutaneous Metastasis: Metastatic disease to the skin from internal cancers (e.g., breast, lung) can present as rapidly growing nodules and is critical to identify due to its implications for prognosis and treatment.

Dermatofibrosarcoma Protuberans: A rare, low-grade sarcoma that can grow rapidly and appears as a firm, nodular mass, often with a violaceous color.
Atypical Fibroxanthoma: A rare, low-grade sarcoma that typically occurs in sun-damaged skin of older adults, presenting as a rapidly growing, firm nodule.
Leiomyosarcoma: A rare, malignant tumor of smooth muscle origin that can occur in the skin, presenting as a rapidly growing nodule.