Effect of freezing on histologic grading of invasive ductal breast cancer

OBJECTIVE: To quantify the histologic changes caused by freezing during tissue processing and their influence on histologic malignancy grading as a prognostic factor in invasive ductal breast cancer. STUDY DESIGN: We studied frozen and nonfrozen formalin-fixed, paraffin-embedded samples of 18 cases of invasive ductal breast cancer. Features associated with histologic malignancy grading of breast cancer--i.e., nuclear pleomorphism, mitotic index and tubular differentiation--were assessed by quantitative morphometric methods. RESULTS: In our material, frozen samples consistently had a smaller mean nuclear profile area than nonfrozen samples (mean difference, 32%). Frozen nuclei were also clearly less symmetric and uniform in shape than non-frozen nuclei. Moreover, frozen samples had consistently higher mitotic indices than nonfrozen samples (mean difference, 66%, with the standardized mitotic index). Tubular differentiation, as expressed in fraction of fields with tubular differentiation, increased by 16% as a result of sample freezing. CONCLUSION: According to our results of morphometric measurement in invasive ductal breast cancer, great caution should be exercised when prognostic conclusions are based on frozen tissue samples.