Four stages of the evolutionary progression of cancer:

Initiation→Cancer progression → Evasion of cancer cell elimination  → Tumor growth and dispersal 

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#Unit 4. Cell Communication and Cell Signaling

Carcinogens can be classified into two categories: 

1. Direct-acting carcinogens

2. Indirect-acting carcinogens

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#Unit 4. Cell Communication and Cell Signaling

Direct-acting carcinogens

highly reactive compounds that can react with and modify nucleotide bases in DNA, to distort the normal pattern of base pairing.

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#Unit 4. Cell Communication and Cell Signaling

Direct-carcinogens includes:

Ethylmethane sulfonate (EMS)

Dimethyl sulfate (DMS)

Nitrogen mustards

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#Unit 4. Cell Communication and Cell Signaling

Indirect-acting carcinogens 

Relatively unreactive compounds that become modified to more reactive forms by cellular cytochrome P-450 enzymes

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#Unit 4. Cell Communication and Cell Signaling

Benzo(a)pyrene

(found in cigarette smoke & coal tar) undergoes metabolic activation by cytochrome P-450 in the lungs to form a potent mutagen

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#Unit 4. Cell Communication and Cell Signaling

P-450 enzymes, modify benzo(a)pyrene in a series of reactions, producing 7,8-diol-9,10-epoxide, a highly potent mutagenic species