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TABLE H-1 Examples of Common Predisposing Factors

Predisposing Factor

Mechanism Influencing Susceptibility to Cancer

A.

Temporal Factorsa

 

Circadian rhythms

 

Changing ingestion and inhalation characteristics during life

 

Depression and stress

 

B.

Nutritional Factorsb

 

Vitamin A and iron deficiencies

May increase susceptibility to carcinogenic hydrocarbons

Dietary-fiber intake

Insufficient intake may increase residence time of carcinogens in contact with epithelium of digestive tract

Alcohol intake

May affect susceptlbility through effect on liver

C.

Concurrent Diseasesc

 

Respiratory tract infections and bronchitis

May predispose lungs to cancer by disturbing pulmonary clearance or promoting scarring

Viral diseases, e.g., Hepatitis B

May activate proto-oncogenes and cause liver necrosis and regeneration

Hypertension

May increase the potential for DNA damage in peripheral lymphocytes

aData from Fraumeni, 1975; Borysenko, 1987.
bData from Calabrese, 1978.
cData from Warren and Weinstock, 1987.

cyclic aromatic hydrocarbons (PAHs). Interindividual variation by a factor of several thousand has been observed in placental aryl hydrocarbon hydroxylase (AHH) activity, which is catalyzed by CYP1A1; some of this variability is under direct genetic control, but variations also result from an enzyme induction process due to maternal exposure to environmental carcinogens, such as tobacco smoke. A genetic polymorphism in CYP1A1 in which an amino acid substitution in the heme-binding region of the protein increases catalytic activity of PAHs has been linked to enhanced susceptibility to squamous cell carcinoma of the lung in cigarette-smokers (Nakachi et al., 1991). Japanese with the suscepti-



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