The effect of tissue fixation and processing on breast cancer size.

Precise measurement of an invasive breast cancer is crucial for pathological staging and subsequent patient management. Formalin fixation and histological processing may change tissue size, but there is no agreement on which state of the specimen, fresh or fixed, should be used for final tumor measurement. To determine the influence of fixation and processing on breast tumor size, a specific 1-dimensional measurement from 50 invasive breast tumors was recorded in fresh, fixed, and processed/mounted states. Tumors varied in maximum measured dimension from 4 to 20 mm and contained 10% to 90% estimated fibrous tissue (mean, 52.8%). In 96% of cases, there was no difference in measured size between fresh and fixed states. After final processing and mounting, a decrease in size from initial fresh measurement was noted in 40% of cases (mean difference, 2.4 mm; maximum difference, 7 mm). In 9 cases (18%), the measured size increased by a maximum of 3 mm (mean, 1.7 mm) after processing/mounting. Twenty-one cases (42%) showed no change in measurement during the entire fixation and processing protocol. Increases in measured size were attributed largely to tissue expansion during histological sectioning/mounting. One can arguably measure the size of an invasive breast cancer from either the fresh or fixed state without affecting accuracy, but caution should be exercised in relying solely on the microscopic measurements.