How is the tumor size defined in breast cancer pathology?

Updated: Mar 20, 2019
  • Author: Oudai Hassan, MD; Chief Editor: Chandandeep Nagi, MD  more...
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Tumor size is measured as the largest dimension of the invasive tumor only, in millimeters.

Practical considerations

When available, the pathologic tumor size takes precedence over the clinical tumor size. The tumor size reported in the pathology report should reflect the pathologist’s best assessment of the largest dimension of the invasive tumor only. This is usually the microscopic invasive tumor size; however, in many circumstances, correlation with the findings from gross examination, prior specimens, different imaging modalities, and clinical information is needed to most accurately estimate the tumor size. Benign and in situ mass-forming lesions, biopsy site changes, fixation, and processing can all affect tumor size measurements.

Tumor size should be measured with a precision of 1 mm. Tumor size cutoffs of 1 cm and of 2 cm are particularly important for treatment decisions. A statement about how the measurement was obtained or estimated is helpful (eg, "Microscopic, gross, largest dimension in prior core biopsy is…, estimated by…, at least…, likely not more than…, correlation with imaging and clinical findings is needed.").

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