Pitfall in assessing the size of tumor phantoms on mammograms

Abstract

Background: Tumor size is crucial for clinical management and prognosis of breast malignancies.

Materials and methods: The gold standard-size of 12 tumor phantoms was assessed at The Department of Production Engineering. Subsequently, with a conventional ruler, seven experienced mammographers measured the largest diameter of the 12 devices in two independent trials.

Results: In the first trial, 30% (n=25) of the 84 values given by the seven mammographers failed to recreate the gold standard size by >1 mm and in the second, by 37% (31/84). Size was overestimated (>1 mm) in 9.5% (n=8) of 84 measurements in the first trial, and in 15.5% (14/84) in the second. Conversely, size was underestimated (>1 mm) in 20% (n=17) of 84 measurements in the first trial, and in 21% (18/84) in the second. Neither the age of the participants, nor their years of experience improved the obtained results.

Discussion: The method used here raised doubts concerning the ability of discriminating size among subgroups of T1 breast tumors in mammograms. According to the TNM staging system, T1 tumors (≤2.0 cm in greatest dimension) are subdivided into T1mic: microinvasion (≤0.1 cm), T1a (>0.1 cm but not more than 0.5 cm), T1b (>0.5 cm but not more than 1.0 cm) and T1c (>1.0 cm but not more than 2.0 cm in their greatest dimension). Since the TNM staging system for breast tumors is important in therapeutic decision making, it is crucial to develop a more reliable method for tumor size assessment.