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concept: induction and proliferation
classification of tumors
derived from either: (distinct subsets with respect to biological behavior)
| • | epithelial or connective tissue |
| • | blood forming and immunocytic tissues |
| • | CNS and PNS derived (glial cells, Schwann cells, and in rarer instances, ependymal and embryonic neuroblast tissues)
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Benign:
| • | adenomas: glandular epithelium (of all 3 germ layers) |
| • | papilloma: squamous epithelium |
| • | fibroma, chondromas, osteomas: connective tissue |
Malignant:
| • | adenocarcinoma (carcinoma): glandular epithelium (of all 3 germ layers) |
| • | sarcoma: connective tissue (fibrosarcoma, chondrosarcoma etc…) |
anaplastic: used to describe tumors that do not resemble any known tissue (i.e. can’t determine origin)
| • | cell cycle of tumor cells ~ same length of time as normal cells |
| • | it’s the increase in fraction of tumor cells in division at any one time compared to normal tissue that gives expansive growth |
| • | tumor grows excessively because there are both larger numbers of cells growing at any one time and fewer cells undergoing terminal differentiation or apoptosis |
p53 gene
| • | “guardian of the genome” (DNA damage induces p53 à halts the cell cycle in G1) |
| • | transfection with mutant p53 “immortalizes” cells |
| • | the p53 mutations induced by UV radiation are found in >90% of human SCC’s and are present in AK’s |
c-kit gene
| • | encodes the cellular receptor tyrosine kinase for the ligand stem cell factor (AKA mast cell growth factor) |
| • | involved in pathogenesis of: mast cell disease, and piebaldism |
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