Pitfall in assessing the size of tumor phantoms on mammograms

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

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.

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.

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.