Abstracts 4 0 7

variable selection. Of 427 Ph-positive patients, 367 patients had complete data for all 17 variables and could be included in the analysis. Concordance between the methods of analysis could be shown in the respect that of seven prognostically significant variables, five were common to both methods. The results complement each other in the sense that a maximum of information is gained about the study population.

A20 VALIDATION OF SURROGATE OUTCOMES FOR EVALUATION

OF CANCER SCREENING INTERVENTION

William E. Barlow Center for Health Studies

Seattle, Washington

Surrogate outcomes have been suggested as a means for reducing the duration of randomized clinical trials by increasing the number of events and their timeliness. Prentice (Statistics in Medicine, 1989) suggested criteria necessary for validation of surrogate outcomes as a substitute for mortality. We propose a statistical model testing these criteria in a study evaluating the efficacy of mammography screening in reducing breast cancer mortality.

Surrogate outcome validity is tested in a population-based cohort of 94,657 healthy women aged 40 or older. Mortality due to breast cancer is the outcome and combinations of advanced tumor stage and size are tested as surrogate outcomes for mortality. The statistical model predicts that the beneficial impact of mammography screening on mortality should be fully captured by the surrogate outcome. There should be no effect of screening on mortafity conditional on the surrogate outcome. The hazard rate is modelled within a semi-parametric framework for the three transitions: "healthy" - > advanced disease; "healthy" -> death due to breast cancer; and advanced disease -> death.

Surrogate outcomes have been proposed for a randomized trial to be conducted in the United Kingdom testing the optimal interval between mammography screening evaluations. Our model permits a test of the validity of those outcomes.

A21 PRINCIPLES OF AGREEMENT FOR POST NDA

CLINICAL TRIALS

Janet T. Holbrook and Curtis L. Meinert The Johns Hopkins University

Baltimore, Maryland

Clinical trials evaluating drugs after approval (post NDA) are assuming a greater role in the drug evaluation process, especially for drugs that undergo expedited review and approval via new FDA regulations. Further, trials involving head-to-head comparisons of competing drugs are often conducted post NDA. Often these types of trial are sponsored by a consortium of publicly funded institutions and pharmaceutical manufacturers.

This presentation will focus on the principles of agreements between independent research groups that conduct publicly funded clinical trials and pharmaceutical companies that provide drugs and, in some cases, funds for the trials. We will survey current multicenter clinical trials of this type and describe the types of agreements under which these consortia operate. We will also review our own experience developing agreements with four drug manufacturers for the conduct of two u'ial of treatments of AIDS-related eye disease. The major focus will be on agreement principles for protocol development and approval, monitoring, data ownership and access, publication and presentation poficies, and composition and function of oversight committees.

A22 DRUG DEVELOPMENT ISSUES IN THE PACIFIC REGION:

COST-EFFECTIVENESS

John A. Derma Bristol-Myers Squibb Pharmaceuticals

Victoria, Australia

The emerging issue of "cost-effectiveness" is strategically important in international pharmaceutical markets. Within the Pacific region, recent guidelines from the Australian regulatory authority have been introduced for gearing new drugs listed on the Federal government's prescription reimbursement scheme.

The purpose of this paper is to review the methodology which pharmaceutical sponsors will