The Case for Screening
The American Cancer Society issued a dire warning last week that progress on the cancer front is slowing. The group notes that prevention and early-detection efforts are in a stall and cites as prime evidence that fewer women are getting mammograms. This lament comes on the heels of new American College of Physicians guidelines earlier this month soft-pedaling routine mammography for women in their 40s, given that thousands of women need to be screened to benefit only a few and false alarms are high. The views of these two societies echo a broader debate about the merits of early-detection efforts. The crux of it is not that tests can't find cancers earlier-they can-but whether they are worth the cost, and if spotting cancer early always matters.
It's hard to question the benefit of early detection endorsed by the ACS for breast, prostate, colon, cervical, and uterine cancer-including a longer life. But what's often missed in the debate is that, in any group, not all patients respond the same to therapy. Those with aggressive tumors resistant to treatment influence a statistical mean that can hide major benefit to others. Also overlooked is just how powerful finding cancers early has been to understanding and treating malignancies. It's no coincidence that the war on cancer has been less successful in aiding those with lung, pancreatic, and ovarian cancer, which typically come to medical attention only after patients develop symptoms of advanced disease. When bloody sputum, intractable backache, or a swollen belly is the first hint of cancer, the disease has spread and is vastly harder to treat. That might change if we learned more about the early stages of these cancers.
Contrast this with the history of colon cancer. Screening colonoscopy has taught us that the precursors of virtually all colon cancers are benign polyps. Removing them prevents the cancer. Look at cervical cancer, where Pap smears revealed that there is an early "in situ" form in which microscopic nests of cancerous cells have not yet invaded nearby tissue. This test has saved countless lives, helped to preserve women's fertility by enabling limited excision of in situ lesions, and now can distinguish benign from cancer-causing strains of the human papillomavirus.
Learning about in situ disease has brought better understanding of breast cancer as well. A condition called ductal carcinoma in situ, or DCIS, was thought to be relatively rare and to infrequently progress to invasive cancer. But mammograms, detecting DCIS long before a lump forms, found it to be much more common and to progress to invasive cancer in over 30 percent of cases, sometimes within five years; in other cases, in two or three decades. This has led scientists to focus on the different forms of this disease, with a keener eye on when and how to intercede with therapy based on its early microscopic appearance, genes, or other biological characteristics.
No wait. The hottest early-detection debate now brewing centers on screening those at high risk for lung cancer, the biggest cancer killer, which at the moment has no accepted test. A low-dose CT scan approach developed by radiologist Claudia Henschke at Weill Cornell Medical College can pick up the tiniest of early-stage invasive lung cancers with few false alarms, limiting the risk of unneeded surgery. It's not clear whether this will save lives. But I've yet to find a physician who would happily wait and watch a small, invasive lung cancer fester rather than have it removed.