Cystic degeneration during neo-adjuvant chemotherapy predicts squamous metaplasia of triple negative breast cancer: report of two cases.

Neo-adjuvant chemotherapy (NAC) has become a standard treatment for advanced breast cancer because of the advantage of monitoring drug sensitivity and enabling breast-conserving therapy. The changes during NAC are also important to know the biological characteristics of the tumor. We experienced two cases with cystic degeneration and enhancement of the cyst wall during NAC for triple negative breast cancer (TNBC). They were diagnosed to have breast cancer with squamous metaplasia. In case 1, a 37-year-old woman with right breast cancer diagnosed as TNBC, T3N3M0, Stage 3b was treated with NAC. MRI showed a cystic degeneration with a diameter of 3.5 cm and enhancement of the cyst wall, and the other nodules were extinguished. The histopathological finding of the surgical specimen revealed solid tubular carcinoma with squamous metaplasia. In case 2, a 58-year-old woman with right breast cancer diagnosed as HER2 enriched subtype, T2N0M0 stage 2 was treated with NAC containing trastuzumab. The post-NAC MRI showed extinguishment of the mass in the right breast, but showed a cystic lesion with 24 mm in diameter and enhancement of its wall in the left breast. She underwent breast conserving surgery for bilateral breast cancer, and histopathological finding of the surgical specimen indicated complete remission of right breast cancer and squamous cell carcinoma developed in the left breast. These changes are impressive and remind us that there are metaplastic changes (especially for squamous metaplasia) with resistance to chemotherapy.