There is a paucity of peer-reviewed studies assessing the clinical knowledge and use of the eight tests we investigated. Of all of the tests, BRCA has been the most studied, yet it remains underutilized. Indeed, our study suggests the likely underuse of certain tests (e.g., BRCA and MMR), which are recommended for risk stratification in people at high risk for breast, ovarian, and colorectal cancers. It also highlights important barriers to appropriate testing, such as lack of confidence in genetics knowledge and lack of familiarity with recommended genetic tests (e.g., KRAS testing when deciding whether to treat a patient with cetuximab). Additionally, our study suggests the appropriately low use of tests where there are either guidelines recommending against use, guidelines stating that there is insufficient information to recommend for or against use, no guidelines, or conflicting guidelines (e.g., OncoVue, fecal DNA, breast cancer tumor gene expression profiles, CYP2D6, and UGTA1).
The most common reason offered by clinicians for ordering or recommending BRCA and MMR was that the patient met practice guidelines, indicating that many providers are aware of national recommendations regarding genetic testing and consider these recommendations in making decisions about testing. Still, in settings where testing would be recommended by multiple national organizations, a sizable portion of clinicians make no reference to practice guidelines as a basis for ordering or recommending BRCA or MMR testing, suggesting that substantial gaps in awareness remain.
It is also worth noting that many providers reported ordering or recommending BRCA
testing in response to requests from patients. A 2003 study assessing the impact of a pilot direct-to-consumer marketing campaign for BRCA
testing in Atlanta, Denver, Raleigh-Durham, and Seattle found that providers perceived an increase in patient awareness of testing, noted an increase in patient requests for testing, and ordered more BRCA
tests, but there was no change in rate of referral to genetic specialists [26
]. Such referrals allow patients considered to be at high risk to receive guidance from a health professional well grounded in cancer genetics about what tests would be most appropriate, as well as pre- and post-test counseling [8
]. Providers who do not specialize in genetics would seem to be important sources of such referrals. However, we found that one-third to one-half of primary care and naturopathic providers in our sample did not make such referrals, even when they suspected patients were at an increased risk for serious hereditary cancer syndromes.
Our finding that providers are using several genetic tests for which there are no practice guidelines highlights the need for further evaluation to determine the clinical usefulness and appropriate role of these genetic tests, including several addressed in our survey. There is some evidence that gene expression profiling tests (e.g., Oncotype
DX, MammaPrint, and H/I ratio) may help estimate risk of recurrence and guide treatment decisions [12
]. Testing for CYP2D6
genotypes are intended to identify individuals with altered functionality in genes that effect drug metabolism. Some authors have concluded that these tests may be useful to health care providers in deciding which treatments to recommend [13
]. However, evidence for the clinical utility of CYP2D6
testing is not conclusive and evidence-based national guidelines have not endorsed these tests [7
If a test proves to be cost effective and to lead to improved clinical outcomes, it must then be integrated into clinical practice if its potential to reduce cancer morbidity and mortality is to be realized. As we have seen in the case of BRCA
testing, the best known of the eight tests in our study and included in national guidelines for a number of years, such an inclusion is an important but not sufficient part of this process. Other strategies include endorsement by medical societies, creation of decision support tools, and incorporation into current and continuing medical education [19
The lack of confidence by health care providers in their basic knowledge of cancer genetics is noteworthy and is consistent with other studies [17
]. Because of this, there is a higher chance that tests will be ordered incorrectly or inappropriately and may be misinterpreted by a nongenetic specialist, which may significantly hamper proper risk management [34
]. This suggests a need for continued training to give clinicians the necessary background to know when they should order a given genetic test, how to correctly interpret the results, and in what situations patients should be referred to a genetic specialist. The higher level of confidence in breast and ovarian cancer genetics among OB-GYNs is not surprising and is consistent with research by Trivers et al., who found that being an OB-GYN was a predictor of appropriate referral to genetic specialists [35
]. Others have found that specialists, such as oncologists and OB-GYNs, are often more knowledgeable about cancer genetics and cancer risk assessment than primary care providers [26
]. Low levels of confidence in personal knowledge of cancer genetics, coupled with lower rates of referral to genetics specialists for high-risk patients emphasize the need for further medical genetics training, especially among primary care providers and naturopaths.
There are several limitations to this study. Firstly, given our cross-sectional study design, we could not infer causality from our data. Secondly, the survey answers were self-reported and therefore subject to recall bias. Thirdly, differences in the time interval we used for different tests in asking clinicians whether they had ordered or recommended the tests (i.e. “ever” or “in the last twelve months”) limit our ability to compare the use of all eight genetic tests amongst each other. Due to small sample sizes, we were not always able to present results for the genetic tests by provider group. Finally, we did not collect information about the nature of therapy offered by respondents who reported treating breast, ovarian, and colorectal cancer. This makes reported differences in the frequency of treating such patients difficult to interpret. Higher rates of cancer treatment reported by naturopaths compared with primary care providers or OB-GYNs may involve the perception that naturopathic efforts to improve the patient's overall health are a component of cancer treatment, a view that may not have been shared by most allopathic clinicians providing services other than surgery or chemotherapy.