Benign tumors are usually well-differentiated and well-demarcated, with low mitotic activity, no metastases, and no necrosis.

Malignant tumors (cancers) may show poor differentiation, erratic growth, local invasion, metastasis, and apoptosis. High mitotic activity.

Fat tumors:

• Lipoma: benign, low mitotic activity
• Liposarcoma: malignant, increased mitotic activity

Lipomas/Liposarcomas are the commonest soft-tissue tumors in adults. The high mitotic index & infiltrative nature indicate that the mass is malignant.