An abnormal mass of tissue. Tumors are a classic sign of inflammation, and can be benign or malignant (cancerous).
There are dozens of different types of tumors. Their names usually reflect the kind of tissue they arise in, and may also tell you something about their shape or how they grow. For example, a medulloblastoma is a tumor that arises from embryonic cells (a blastoma) in the inner part of the brain (the medulla).
Diagnosis depends on the type and location of the tumor. Tumor marker tests and imaging may be used; some tumors can be seen (for example, tumors on the exterior of the skin) or felt (palpated with the hands).