Neoplasia means literally “new growth” Not all new growths are neoplasms “Tumor” originally meant “swelling”; now it is synonymous with neoplasm Oncology is the study of tumors Neoplasms may be benign or malignant Malignant neoplasms are cancer Willis defined a neoplasm as an abnormal mass of tissue, the growth of which exceeds and is uncoordinated with that of the normal tissues and persists in the same excessive manner after cessation of the stimulus which evoked the change. Robbins adds that the abnormal mass is purposeless, preys on the host, and is virtually autonomous.

Stages of neoplastic evolution 1. Physiologic growth: persistent, periodic, blastic, regenerative. e.g. Squamous metaplasia, nevus, enterocyte, lymphocyte 2. Dysplasia; abnormal growth and differentiation. e.g. Intraepithelial neoplasia I and II, dysplastic nevus, aberrant crypt focus, myelodysplastic syndrome 3. Intracompartmental neoplasia. e.g. CIN III = carcinoma in situ, radial growth melanoma, adenomatous polyp, lymphoma 4. Invasive cancer. e.g. squamous carcinoma, vertical growth melanoma, adenocarcinoma 5. Metastatic Cancer

Benign versus malignant neoplasia Well-differentiated although dysplasia is present Progressive, slow growth with normal mitosis Not invasive or metastatic Malignant Aberrant differentiation Erratic growth; abnormal mitosis Invasive and may metastasize

Naming neoplasms Benign neoplasms – generally add “oma” e.g. papilloma, lipoma, leiomyoma Malignant neoplasms – epithelial cells become carcinomas, mesenchymal cells become sarcomas e.g. papillary carcinoma, liposarcoma, leiomyosarcoma Exceptions: e.g.hepatoma, melanoma, lymphoma

Mechanisms of carcinogenesis   Steps and stages initiation promotion progression metaplasia/hyperplasia dysplasia neoplasia/anaplasia

Two-stage model of mouse skin carcinogenesis

Phenobarbital promotes hepatocarcinogenesis Plus phenobarbital Minus phenobarbital