Background: The aim of this study was to examine the effect of measurement bias in breast cancer and to create a more rational T-size categorization in tumor-node-metastasis staging in response to smaller, screen-detected cancers and measurement bias.
Methods: From 1987 to 2003, 10,853 invasive nonmetastatic breast cancers enlisted in the Rhode Island Cancer Registry with a known dimension were reviewed. Data analyzed by proposed classifications included the rate of lymph node metastases and the mortality rate from breast cancer.
Results: The median diameter was 16 mm. Cancer measurements reflected the bias in pathologists' dimension recording, which is centered strongly about whole- and half-centimeter sizes. A new T classification is proposed with the following sizes and frequencies in the Rhode Island Cancer Registry: 1 to 2 mm = T1 mic (3% of registered cases); 3 to 7 mm = T1a (11%); 8 to 12 mm = T1b (23%); 13 to 17 mm = T1c (18%); 18 to 22 mm = T2a (17%); 23 to 27 mm = T2b (8%); 28 to 32 mm = T2c (8%); 33 to 42 mm = T3a (6%); 43 to 52 mm = T3b (3%), and greater than 52 mm = T3c (4%). The unadjusted odds ratio for the probability of node metastases was 1.43 (confidence interval, 1.40-1.46; P < .001) with each increase in proposed grouping. The range in the lymph node metastatic rate was 5.5% for tumors 1 to 2 mm to 64% for cancers greater than 52 mm. By Cox proportional hazard, the unadjusted hazard ratio for death from breast cancer for each increase in proposed grouping was 1.33 (confidence interval, 1.29-1.37; P < .001). The 10-year survival rate ranged from 98.3% for tumors 1 to 2 mm to 70.3% for cancers greater than 52 mm.
Conclusions: A more rational T category for use in tumor-node-metastasis staging is presented to reflect the much smaller invasive breast cancers encountered by screening and to account for the dimension recording bias of pathologists. This new T category shows a clinically and statistically significant linear relationship for both incidence of lymph node metastases and hazard ratio of death.