Devita, Hellman, and Rosenberg's Cancer

LWBK1006-03 LWW-Govindan-Review November 24, 2011 11:19

Chapter 3•Etiology of Cancer Part 1 53

Answer 3.39. The answer is B.

SV40 DNA or antigens have been detected in some human cancers, includ-

ing mesotheliomas, osteosarcomas, and brain tumors. The major source

for human exposure to this virus was through contaminated poliovirus

vaccines administered from 1955 to 1963. However, there is no epidemi-

ologic evidence that individuals exposed to these contaminated vaccines

have increased risk of cancer. In the only double-blind study conducted,

there was no correlation found between SV40 and human tumors. Human

polyomaviruses BK and JC are ubiquitous, and there have been occasional

reports linking these viruses to human cancers. However, comprehensive

analysis of the data suggests no convincing evidence of an association.

Answer 3.40. The answer is D.

Both innate and adaptive immunity play a role in immune surveillance of

tumors. Adaptive immune cells, T and B lymphocytes, along with their

effector molecules, innate immunity cells (e.g., natural killer cells), and

proinflammatory cytokines (e.g., IL-12) are all important for immune

surveillance of tumors. In animal models, deficiency of different inflam-

matory or immune mediators leads to different tumors, suggesting that

the immune surveillance mechanisms differ for tumors arising in different

tissues. Immune surveillance of tumors may or may not be dependent on

antigens expressed on the tumor. In addition, antigens expressed on tumor

stroma or certain self-antigens may be relevant for immune surveillance.

Answer 3.41. The answer is C.

More than a century ago, studies showed that infection with

inflammation-causing bacteria induced dramatic regressions of cancers.

An important role for immune surveillance of tumors is suggested by

increased incidence of certain tumors in organ transplant recipients

receiving immunosuppressive therapy. Nonmelanoma skin cancers are

increased 50-fold in these patients, but the risk of melanoma is increased

only modestly. Immunosuppressive therapy has a differential effect on

various aspects of the immune system, and different components of the

immune system are relevant for surveillance of the various tumors. This

differential effect may account for the differences in the risk for the various

tumors in immune-suppressed patients. The presence of tumor-infiltrating

lymphocytes, particularly T cells in tumors such as melanomas, colon

cancers, and ovarian cancers, is associated with improved prognosis sup-

porting the role of immune surveillance in limiting tumor progression.

Tumor progression is also controlled in many patients by the autoim-

mune response that leads to paraneoplastic neurologic syndromes.

Answer 3.42. The answer is C.

Many lines of evidence support the association of inflammation and can-

cer. In general, acute inflammation has a greater capacity to eradicate

tumors, whereas chronic smoldering inflammatory conditions that lead

to infiltration of the tissue stroma by inflammatory cells could be associ-

ated with tumor initiation and progression. Thus, in conditions such as