Devita, Hellman, and Rosenberg's Cancer

LWBK1006-04 LWW-Govindan-Review November 24, 2011 11:19

Chapter 4•Etiology of Cancer Part 2 65

Answer 4.12. The answer is D.

The latent period is defined as the time between the radiation exposure

and the development of a radiation-induced tumor. Acute and chronic

myelogenous leukemias are sensitive to induction and their peak latent

period is usually around 4 to 8 years, although cases as early as 2 years

have also been reported. For solid tumors, the latent period is typically

longer and can even exceed two decades.

Answer 4.13. The answer is D.

Studies at the molecular and cellular levels and epidemiological data have

helped derive two dose-response models of radiation interaction. First is

the linear model wherein cancer risk is directly proportional to radiation

dose. In the linear-quadratic model, the risk is proportional to dose at

low dose and rapidly increases with high doses.

Answer 4.14. The answer is C.

High LET results in few energy tracks in the cell. Although few, they have

a high density that is sufficient to produce complex effects. The dose-

response relationship in this case is linear because of the higher effective-

ness of this type of radiation. Radon exposure (e.g., in uranium mines) is

an example of high LET.

Answer 4.15. The answer is B.

Radon is a naturally occurring high LET radiation found in rocks and soil.

It is chemically inert and uncharged, but spontaneous decay results in its

progeny, which are radioactive and electrically charged. The latter can

attach to ambient dust particles, which when inhaled can result in lung

irradiation. This is a well-defined etiologic factor in the development of

lung cancer. Bystander effect is an interesting feature observed with radon

wherein the cells exposed to radon send out signals to adjacent cells, which

are not exposed. These signals result in mutagenic and oncogenic changes.

Answer 4.16. The answers are (A) 1, (B) 2, (C) 4, (D) 3.

The age at time of exposure plays a critical role in cancer induction.

Younger age at exposure increases the risk substantially when compared

with middle age of exposure. Good examples are breast cancer and thy-

roid cancer. When compared with middle-aged women, young children

and adolescents have a higher risk of developing breast cancer after expo-

sure to radiation. The defects involved in ataxia-telangiectasia may be

involved in radiation-induced breast cancer secondary to increased radi-

ation sensitivity.

Answer 4.17. The answer is D.

Age plays an important role in induction of second cancers because chil-

dren are more susceptible to radiation. Because children have a smaller

body size, multiple organs may be exposed, as the area exposed to radia-

tion is large. Genetic susceptibility is an important factor in induction of