slide set 21 Flashcards
cancer cells are defined by:
reproduce without, or in defiance of, normal signals
invade and colonize areas reserved for other cells
non-cancerous somatic cells facts
- cells need signals to survive
- cells need signals to grow and divide
- cells need to adhere to a surface or other cells (or other proteins)
- damaged cells will activate apoptosis
cancer cells ignore all this!
how does a tumor begin
with one cell
microevolution
carcinomas
cancer of epithelial cells
80% of cancers are epithelial in origin
this is because epithelial cells are more exposed to elements (more on the surface)
sarcomas
connective or muscle cancer
leukemias and lymphomas
blood cell cancers
benign tumor
“oma” ex: adenoma
malignant
for epithelial, “carcinoma” EX: adenocarcinoma
for connective/muscle, “sarcoma” EX: chondrosarcoma
also over-profileration, but some cells escape basal lamina and can move beyond the cell
tumor cell population
cancer starts with a single cell
- but that cell reproduces and mutates as time passes
- mutations within the growing population:
- select for the fastest growing and least inclined to respond to signals
clonal origin
cancer starts with a single cell
evidence for clonal origin
- chronic myelogenous leukemia
- begins with rare event that leads to forming of Philadelphia chromosome
- all patients have a chromosome translocation between chromosomes 9 and 22 in all of the tumor cells
- creates a novel enzyme
- all patients with this type of cancer: every cell has the philadelphia chromosome
because cancer arises from a single cell, changes must be heritable (2 explanations)
- Must be mutation to genes
- somatic mutations because they occur in somatic cells (cells of the body) not germ cells (cells that will form eggs or sperm)
- Epigenetic changes
- heritable changes in gene expression from chromatin structure
- heritable = passed down to daughter cells, not offspring
- heritable changes in gene expression from chromatin structure
evidence that multiple mutations are required to turn a cell cancerous
- cancer incidence rises with age
- if a single mutation was sufficient and equally likely at any time, we would expect a linear rate of incidence
- instead, cancer requires multiple mutations before all normal regulatory controls are lost
2 big summarizing features
- cancer develops from a single cell
- multiple mutations are required to transform a cell
these were confirmed by sequencing entire genomes of single cells within a tumor
clonal evolution
- accumulation of mutations over time: slow at first
- tumor progression is an evolutionary process as new mutations increase cell proliferation
- there are sub-clones within tumors
- genetic diversity within a tumor