Association Versus Causation Versus Quality Improvement: Setting Benchmarks for Lymph Node Evaluation in Colon Cancer

There has been substantial attention and interest directed toward improving the quality of medical care in the United States; the need for quality improvement has reached the consideration of policy makers, providers, payers, and patients. In response to congressional mandates, the Institute of Medicine launched the Redesigning Health Insurance Performance Measures, Payment, and Performance Improvement Project ( 1 ), with the goal of accelerating the diffusion and pace of quality improvement efforts. Specific policies have been promoted to improve care, including measurement and reporting of performance data, payment incentives, and quality improvement initiatives. Measures in oncology are under active development, and as this process evolves, it is likely that implementation of performance measures will become mandatory and that the scope will broaden. Lymph node evaluation is a frequently discussed potential quality measure for colon cancer, and benchmarks for adequacy of lymph node evaluation have been proposed. As Chang et al. ( 2 ) point out, “the number of lymph nodes recovered from a patient with colon cancer has been identified as a potentially important measure of the quality of cancer care by many organizations, including the American College of Surgeons, the American Society of Clinical Oncology, the National Comprehensive Cancer Network, the National Quality Forum, healthcare insurance providers, and others.” This paper, a systematic review of the evidence associating lymph node harvest in colon cancer and clinical outcomes is, therefore, both timely and topical. In a pooled analysis including more than 60000 patients ( 2 ), the authors found that 16 of 17 national and international studies demonstrated improved survival as the number of lymph nodes evaluated increased in patients with stage II colon cancer. In addition, four of six studies reported a positive association between lymph node number and survival among patients with stage III colon cancer. The authors conclude that given the evidence, lymph node evaluation deserves consideration as a quality measure for colon cancer care. However, before lymph node benchmarks are established as a quality measure, two important questions must be addressed. First, who or what is being evaluated when we report lymph node counts—the surgeon, the pathologist, the hospital, the patient, or even the tumor? Because each component may have an influence on the overall lymph node harvest, it will be a major challenge to establish whose quality we are measuring. Second, on a more fundamental level, will quality improvement projects aimed at increasing reported lymph node number actually lead to improved patient outcomes? That lymph node number is associated with survival seems beyond dispute; however, no research has determined the mechanism underlying this association. Although best studied in colon cancer, there is a substantial volume of literature demonstrating that the number of lymph nodes evaluated is associated with survival for many cancers. For example, a higher number of lymph nodes evaluated is associated with improved survival in gastric ( 3 ), bladder ( 4 ), lung ( 5 ), esophageal ( 6 ), pancreatic ( 7 ), and breast ( 8 ) cancer. The main mechanism proposed to explain this association is upstaging, in which a more thorough lymph node evaluation results in more accurate determination of lymph node status. With better prognostication, survival improves by stage and, if treatment depends on lymph node status, then treatment may be altered for those patients who are upstaged. However, in reality, the mechanism(s) underlying the association between survival and lymph node number is unknown. For colon cancer, large multicenter ( 9 ) and population-based ( 10 ) studies have not demonstrated an increased proportion of lymph node–positive patients in the setting of larger lymph node harvests, indicating that for this disease, upstaging is an inadequate explanation of the phenomenon. Alternatively, the number of lymph nodes evaluated may be a reflection of the adequacy of surgical care; better surgery may be directly related to survival. However, the relationship between lymph node number and survival is consistent not only for cancers in which survival appears to be directly related to quality of surgery but also for cancers in which outcome is less dependent on surgical technique. The number of lymph nodes present (and therefore evaluable) in a given individual is not fixed but varies between individuals, is influenced by patient and tumor factors, and is modifiable. In fact, it is likely that the number of lymph nodes evaluated in a given patient reflects, at least in part, the underlying interaction between tumor and host, and this interaction itself may have important prognostic implications. The lymph node microenvironment has a primary function in immunologic surveillance, enabling immunologic responses of the host to the tumor. A recent study ( 11 ) has demonstrated that the presence of high levels of immune cells within colorectal cancers is associated with the absence of metastatic invasion, a less advanced pathologic stage, and increased survival. The number of negative lymph nodes may serve as a marker for tumor–host immunologic interactions, which may ultimately predict disease recurrence. Thus, there is increasing evidence that the explanation for survival improvements associated with greater number of evaluated lymph nodes is not only related to upstaging or quality of care. Indeed, the number of negative lymph nodes evaluated is likely an independent prognostic factor in colon cancer reflecting tumor biology. Simple solutions for quality improvement (such as setting quality benchmarks for number of lymph nodes evaluated in colon cancer) are attractive to policy makers and payers. However, if such solutions are not based on sound evidence, they are likely to fail to achieve improvements in patient outcomes and, worse, may divert attention from effective strategies. We are in the era of quality improvement, and clinicians should welcome programs that ensure that every patient receives high-quality cancer care. It is, however, essential that quality improvement initiatives are subject to standards of evidence that reflect the tremendous expenditures of money and human resources required for their implementation.

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