Effect of Hydrochloric Acid Decalcification on Expression Pattern of Prognostic Markers in Invasive Breast Carcinomas

In the United States, it is estimated that 100,000 people are living with metastatic breast cancer (BC) with bone representing the most common site of involvement. However, patients with isolated bone metastasis at presentation may have a longer survival. Therapeutic options for BC bone metastases often include systemic anticancer therapy (endocrine, chemotherapy, monoclonal antibodies, and/or other targeted therapies), which is largely dependent on the immunohistochemical (IHC) repertoire of the cancer for the prognostic markers [estrogen (ER) and progesterone receptors (PR), Ki-67, p53, and Her-2/neu] at its osseous metastatic site. Traditionally, specimens obtained from the bone metastasis require decalcification, which may affect the immunoreactivity of these prognostic markers. To the best of our knowledge, limited studies describe the effect of decalcification on immunoexpression of the above-mentioned markers. A detailed illustration of the effect of decalcification on BC specimens in a real-time manner is lacking in the literature.

Herein, we sought to determine the impact of decalcification on the IHC expression pattern of the above listed markers on BC tissue following decalcification.

After Institutional Review Board approval, sections from the residual tumor specimens were collected prospectively from 15 BC excision specimens and 1 curetting from a BC bone metastasis. The sections (3 to 6 sections/case) for decalcification were collected following routine submission for pathologic evaluation. The sections were subjected to hydrochloric acid (HCl)-based Decal Stat decalcifying solution for 2, 12, 18, and 24 hours in each case. IHC studies for ER, PR, Ki-67, p53, and Her-2/neu were performed on 1 representative section of the regularly processed tumor block and 1 decalcified tumor block from each time point. Scoring of ER and PR were performed according to the Allred scoring system. Scoring of Her-2/neu was performed according to CAP/ASCO guidelines.

The tumors comprised 11 grade 3 invasive ductal carcinomas, 2 grade 2 invasive ductal carcinomas, 2 grade 3 invasive lobular carcinoma, and 1 metastatic BC to bone. Nine cases showed Allred score 8 for ER, 1 case showed Allred score 4, 1 case showed Allred score 2, and the remaining 5 were ER negative. For PR, 1 showed Allred score 8, 2 Allred score 7, 4 Allred score 6, 1 each Allred score 5 and score 2 with the remainder negative for PR. Ki-67 ranged from 5% to 95%. Five cases showed p53 overexpression ranging from 35% to 95%. Five cases each showed 3+, 6 cases showed 2+ Her-2/neu, 3 cases showed 1+ Her-2/neu, and the remaining 2 were negative. All specimens demonstrated decline in ER, PR, Ki-67, and p53 immunoreactivity after 2 hours of decalcification, with additional decline up to 24 hours. The most significant declines in immunoreactivity occurred with Ki-67 and p53. Most of the Her-2/neu cases with an equivocal score declined to zero after 24 hours of decalcification. However, 3 out of 11 cases showing Her-2/neu overexpression remained at the baseline scoring even after extended (24 h) decalcification.

Our results demonstrated that the decalcification process affects the immunoreactivity of the prognostic BC markers. There is progressive loss of reactivity at 2 hours and beyond for markers with lower degrees of expression. In addition, heterogeneity in marker distribution progressed from diffuse to more focal beyond 1 hour.