Malignant Neoplasms

A malignant neoplasm is composed of cells that look less like the normal cell of origin. It has a higher rate of proliferation. It can potentially invade and metastasize. Malignant neoplasms derived from epithelial cells are called carcinomas. Those derived from mesenchymal (connective tissue) cells are called sarcomas. Malignant brain neoplasms and neoplasms of the immune system are special categories with complex nomenclature.

Thus, characteristics of malignant neoplasms include:

• More rapid increase in size

• Less differentiation (or lack of differentiation, called anaplasia)

• Tendency to invade surrounding tissues

• Ability to metastasize to distant tissues

Cytologic features of malignant neoplasms include:

• Increased nuclear size (with increased nuclear/cytoplasmic ratio--N/C ratio).

• Variation in nuclear or cell size (pleomorphism).

• Lack of differentiation (anaplasia).

• Increased nuclear DNA content with subsequent dark staining on H and E slides (hyperchromatism).

• Prominent nucleoli or irregular chomatin distribution within nuclei.

• Mitoses (especially irregular or bizarre mitoses).

All of these features are "atypical" microscopic findings. Atypia implies a change for the worse from normal.

Spread of Malignant Neoplasms

• By direct extension (invasion) into surrounding tissues.

• Through lymph channels to lymph nodes (lymphatic spread)--typical of carcinomas.

• Via the bloodstream (hematogenous spread)--typical of carcinomas or sarcomas.

• Within body cavities (seeding)--typical of neoplasms impinging upon body cavities, such as the peritoneal cavity.