The Effects of Physician Supply on the Early Detection of Rectal Cancer

Could the association between late-stage diagnosis and increased specialty physician supply have resulted from referral of patients with late-stage disease to specialists? If physician supply had been assessed at the locations where cancers were diagnosed, then referral patterns could have contributed to this finding. The effects of physician supply were assessed according to the patients’ residences, however, not the location where their cancer was diagnosed and should not have been affected by referral patterns.

Could the association have resulted from a greater supply of specialists uncovering more cases of existing late-stage disease? This could conceivably occur for slow growing tumors such as prostate cancer, but would not be expected for more aggressive tumors, such as colorectal cancer. Late-stage colorectal cancers not diagnosed in 1 year will become evident in subsequent years through overt symptoms or death. If the association between late-stage colorectal cancer diagnosis and specialty supply was due to increased detection, one would also expect to find a substantial association between stage at diagnosis and the supplies of gastroenterologists. We did not find that association.

The other possible explanation for these findings is that the relationships observed were the result of confounding with some other factor. The multivariate models, however, controlled for patients’ age, sex, race-ethnicity, marital status, comorbidity, type of health insurance, and community measures of socioeconomic status. It is unclear what other factor would be related to stage at diagnosis and have separate and opposite associations with primary care and specialty physician supply.

There is increasing interest in understanding the differences between specialty and primary health care services. Some studies have found no difference in outcomes between the 2 systems of care,^63-66 while others have suggested additional health benefits to specialty care.^66-68 Most have found that primary health care services were less expensive.^67,70,71

The full value of primary care may result from addressing other health care needs in addition to a specific illness.⁷² Stange and colleagues,⁷³ for example, found that family physicians addressed at least one US Preventive Services Task Force recommendation for preventive care in 39% of visits for chronic illness. Recent evidence suggests that most specialists are not likely to address health care needs outside their specialty.^46,74 Medical subspecialists who are serving as patients’ primary providers, however, may be similar to generalists in their delivery of preventive care. Future studies are needed to examine physician supply by type of subspecialty and by other physician characteristics related to the delivery of preventive care.^75-78

Several investigators^9,11 have argued that the balance between primary and specialty physician supply is irrelevant and that the population level supply of primary care physicians is the only measure important for policy. Our results do not support this premise and suggest that the balance between primary care and specialty physician supplies may well affect important health outcomes.

Among the primary care specialties examined, an increasing supply of general internists was associated with earlier stage detection of colorectal cancer, while the opposite was true for the supply of obstetrician/gynecologists. General internists and family physicians may be more likely to include colorectal cancer screening in their practice than are obstetrician/gynecologists, which would explain our findings among women.^31-33,79,80 Obstetrician/gynecologists, however, have shown consistently higher rates of screening for breast and cervical cancers.^76,77,79,81 In addition, obstetrician/gynecologists may not assume the role of primary provider for older women who are at the greatest risk of colorectal cancer.⁸²

Limitations

This study has a number of potential limitations. First, socioeconomic status was not measured at the individual level. Previous studies, however, have validated the use of aggregate measures of socioeconomic status.^38-41

Although physician supply is an important variable relevant to health care policy, it can be considered only an aggregate measure of individual patients’ use of physician services. In future research it will be important to measure actual use of physician services at the individual patient level to confirm these relationships. Finally, our study was restricted to incident cases of colorectal cancer in Florida, which may not be representative of other diseases or other parts of the country.

Conclusions

We found that an increasing supply of primary care physicians was associated with earlier detection of colorectal cancer. Increasing specialty physician supply, however, was associated with later-stage detection. These findings suggest several potential policy recommendations that would improve health outcomes. In the short term, specialists should be aware of these findings and look at health screening practices within their own patient populations. This is particularly important if they are acting as the primary care physician, whether by their own choice or by default. Similarly, patients who have a specialist acting as their primary care physician should either see a family physician or internist for their ongoing preventive care or ask their specialist for the appropriate screening tests.