These requirements are necessary, but not sufficient to prove the effectiveness of screening, which requires demonstration of a decrease in cause-specific mortality. For example, these two criteria are met in the case of screening for childhood neuroblastoma by assessment of urinary catecholamine metabolites. Over that 12 year period, the annual incidence of neuroblastoma in children under age 1 increased from about 28 to 260 per million. No significant reduction in incidence occurred for children over age 1. There was no reduction in mortality for the disease.
Observation is the most widely available examination for the detection of cancer.
It is useful in identifying suspicious lesions in the skin, lip, mouth, larynx, external genitalia, and cervix. The second most available detection procedure is palpation. It is particularly valuable in detecting lumps, nodules, or tumors in the breast, mouth, salivary glands, thyroid, subcutaneous tissues, anus, rectum, prostate, testes, ovaries, uterus, and enlarged lymph nodes in the neck, axilla, or groin. Internal cancers require an extension of observation through endoscopes, x-rays, magnetic resonance imaging, and ultrasound. Laboratory tests, such as the Pap smear, and occult blood testing of the feces have also proven helpful for some of these cancers.