Dupuytren's Nodule: This is the most common diagnosis for a hard mass in the palm. Dupuytren's disease is a condition that affects the palmar fascia, leading to the formation of nodules and cords that can cause the fingers to curl into the palm. The initial presentation is often a small, hard nodule in the center of the palm.

Ganglion Cyst: Although more common on the back of the wrist or on the fingers, ganglion cysts can occur on the palmar surface. They are benign lumps filled with a jelly-like fluid and can feel hard, especially if they are small.
Palmar Fibroma: These are benign growths that can occur in the palmar fascia, similar to Dupuytren's nodules but not necessarily part of Dupuytren's disease. They can present as small, hard masses.
Epidermoid Cyst: These are benign cysts that can form in the skin and sometimes feel hard, especially if they become inflamed or infected.

Squamous Cell Carcinoma or Other Skin Cancers: Although rare, any new or changing skin lesion, especially in sun-exposed areas or in individuals with risk factors, should be evaluated for malignancy. A biopsy may be necessary to rule out cancer.
Infectious Process (e.g., Abscess or Mycobacterial Infection): Infections can present as hard masses, especially if they are deep or chronic. These conditions require prompt diagnosis and treatment to prevent serious complications.

Glomus Tumor: A rare, benign tumor of the glomus body that can occur in the palm. It is usually very painful and sensitive to temperature changes.
Lipoma: Although lipomas are common benign tumors, they are less likely to present as a hard mass in the palm. However, a deep lipoma could potentially feel hard, especially if it is small.
Neurofibroma: Part of neurofibromatosis type 1, these benign nerve sheath tumors can occur anywhere, including the palm, but are relatively rare in this location.