An Evaluation of the Proposed International Clinical Staging System for Cancer of the Breast2

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Abstract
The Committee on Clinical Stage Classification and Applied Statistics of the International Union Against Cancer has proposed a clinical staging system for breast cancer. To evaluate the error involved in the use of this 4-stage system, we have applied it to each of 671 cases as a clinical and also as a “final” system, i.e., one with all available information, including that from surgery and pathology. Inspection of survival curves showed that the proposed system defined 4 distinct stages when applied as a final system. When applied as a clinical system the curves for stages I and II were not clearly separate from one another, nor were the curves for stages III and IV. Frequent sources of error in clinical examination which were important to staging related to (a) state of homolateral axillary nodes in stages I and II, (b) size of primary tumor in stage III, and (c) state of nodes other than homolateral axillary nodes in stage IV. Error (c) was associated with the least experienced examiners. When the clinical staging was corrected for error (c), which presumably would not occur when the most experienced examiners are managing a series of cases, the distinction in the survival curves for the various stages was considerably improved. After this correction it was still noted, however, that 39 percent of clinical stage I cases were final stage II, 34 percent of clinical stage II cases were final stage I, and 52 percent of clinical stage III cases were either final stage I or II. The use of the clinical system in therapeutic trials was considered. It was concluded that in spite of its errors the clinical staging system may be used under various conditions to estimate the magnitude of differences in therapeutic effect that would be observed in the absence of errors in staging.

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