What are the four common classes of malignant tumors?

1. Carcinoma: This is the most common type of malignant tumor. It starts in epithelial cells, such as those lining the skin, lungs, digestive system, and reproductive system.

2. Sarcoma: This type of tumor starts in connective tissue, such as bones, muscles, cartilage, tendons, and lymph nodes.

3. Lymphoma: This type of tumor starts in white blood cells in the lymph nodes.

4. Leukemia: This type of tumor starts in white blood cells in the blood marrow.