Synthesizing medical evidence: systematic reviews and metaanalyses

Systematic reviews and metaanalyses have become increasingly popular ways of summarizing, and sometimes extending, existing medical knowledge. In this review the authors summarize current methods of performing meta-analyses, including the following: formulating a research question; performing a structured literature search and a search for trials not published in the formal medical literature; summarizing and, where appropriate, combining results from several trials; and reporting and presenting results. Topics such as cumulative and Bayesian metaanalysis and metaregression are also addressed. References to textbooks, articles, and Internet resources are also provided. The goal is to assist readers who wish to perform their own metaanalysis or to interpret critically a published example.

Immunotherapy for advanced renal cell cancer

BACKGROUND

The course of advanced renal cell carcinoma is extremely variable, ranging from spontaneous remission to disease progression refractory to chemotherapy. Immunotherapy has held promise of improved outcomes based on uncontrolled studies and randomized controlled trials generally limited by small size and low power.

OBJECTIVES

To evaluate immunotherapy for advanced renal cell carcinoma by comparing: (1) high dose interleukin-2 to other options and (2) interferon-alpha to other options.

SEARCH STRATEGY

A search of MEDLINE, Cancerlit, EMBASE and Cochrane Library databases from 1966 through the end of 1999. Handsearches were made of the proceedings of the annual meetings of the American Urologic Association, ASCO, and biennial European ECCO meetings, and the references of identified studies.

SELECTION CRITERIA

Randomized controlled trials that selected (or stratified) patients with advanced renal cell carcinoma, utilized an immunotherapeutic agent in at least one study arm, and reported response or survival by allocation. Forty-two studies involving 4216 patients were eligible and reported response and 26 of these reported survival outcome (3089 patients).

DATA COLLECTION AND ANALYSIS

Two independent reviewers abstracted each article by following a prospectively designed protocol. Dichotomous outcomes for treatment response (partial plus complete) and for deaths at one year were used for the main comparisons. Survival hazard ratios were also used for studies of interferon-alpha versus controls.

MAIN RESULTS

The average response rate was 10.2 % (range by arm, 0 - 39%) and complete response rate was 3.2% (123/3852; n = 38 studies). Median survival averaged 11.6 months (range by arm, 6 - 28 months) and two-year survival averaged 22% (16 studies, range by arm 8 - 41%). There were no placebo-controlled studies and no randomized controlled studies examined survival for high dose interleukin-2 versus controls. Results from 6 studies (n = 963) indicate that interferon-alpha is superior to controls (OR for death at one year = 0.67, 95% CI 0.50 - 0.89. The pooled hazard ratio for survival of 0.78 (0.67 - 0.90) indicates that the treatment effect persisted until 24 months from randomization. The weighted average median improvement in survival was 2.6 months. Additional comparisons failed to prove a survival benefit from the addition of other agents to either modified schedules of interleukin-2 or to interferon-alpha. Dose-response studies examining survival for either agent could not be identified. The difference in response rate between arms was correlated with the difference in survival (P<0.001) suggesting that response rate difference may be a surrogate intermediate endpoint for survival.

REVIEWER'S CONCLUSIONS

Interferon-alpha provides a modest survival benefit compared to other commonly used treatments and should be considered for the control arm of future studies of systemic agents. Interleukin-2 has not been validated in controlled randomized studies.