The importance of tissue handling of surgically removed breast cancer for an accurate assessment of the Ki-67 index.

Aim: Insufficient attention for the Ki-67 immunohistochemistry has been given to the importance of tissue handling for surgical breast cancer specimens. We sought to investigate the effect of fixation status on the Ki-67.

Methods: We examined the effect of fixative, time to and duration of fixation using surgical specimens, and finally, compared the paired Ki-67 index in the tumour between core needle and surgical specimen.

Results: The Ki-67 was significantly higher when 10% neutral buffered formalin was used (p=0.0276). Insufficient fixation caused a drastic reduction in the Ki-67 index (p=0.0177), but not significant in oestrogen receptor (ER) and human epidermal growth factor receptor 2 (HER2). Sixteen hours delayed time to fixation also caused a reduction of the Ki-67 (p=0.0284), but not significant in ER. Prolonged fixation significantly led to a gradual reduction in the Ki-67 in a time-dependent manner, but not in both ER and HER2. Finally, cutting the tumour before fixation improved fixation status and consequently caused an increased level of the Ki-67 index (p=0.0181), which resulted in a strong correlation of the Ki-67 between core needle and surgical specimen (r=0.8595).

Conclusions: Tissue handling of surgical specimen is critical for assessing the Ki-67 compared with ER and HER2. We should pay more attention to tissue fixation status for the standard assessment of the Ki-67 index.