1. 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.

2. 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

3. 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

4. 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

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

13. Two-stage model of mouse skin carcinogenesis

14. Phenobarbital promotes hepatocarcinogenesis
Plus phenobarbital
Minus phenobarbital