乳癌術前薬物療法後の画像診断の実際：HER2陽性乳癌を中心に

Imaging diagnosis after neoadjuvant therapy for breast cancer：focusing on HER2-positive breast cancer

分子標的薬の登場と進歩により，HER2陽性乳癌の病理学的完全奏効率（pCR rate）は上昇している。さらにトラスツズマブ　デルクステカン（T-DXd）の適応拡大に伴い，HER2低発現乳癌の予後の改善も期待されており，術前薬物療法後の画像評価の重要性は増している。精度の高い画像診断を実現するために知っておくべきこととして，本稿では乳癌サブタイプ別の術前薬物療法後の画像の特徴，HER2陽性乳癌における術前薬物療法後画像評価の実際について解説する。

It is important to be aware that the shrinkage pattern and tendency to remain varies by subtype, when interpreting images after neoadjuvant therapy for breast cancer. The optimal modality for evaluating efficacy is MRI, and interpretation must take the subtype into consideration. Unlike luminal type, in HER2-positive（non-luminal）breast cancer, if contrast enhancement disappears in all phases, there is a high possibility of pCR. Because the specificity of breast MRI is relatively low, if non-mass enhancement is observed in the late phase in the area where the target lesion existed before neoadjuvant therapy, it is difficult to distinguish between residual intraductal carcinoma and post-treatment fibrosis or staining of the original underlying fibrocystic disease. As the indications for T-DXd expand, the prognosis of HER2-low expressing breast cancer is expected to improve, and the importance of image evaluation during and after treatment is increasing.