A compound which is useful as an agent for treating breast cancer is provided. As a result of intensive studies on a compound having a Complex I inhibitory effect and an AMPK activation effect, the present inventors found that a bicyclic nitrogen-containing aromatic heterocyclic amide compounds of the present invention has an excellent Complex I inhibitory effect and the AMPK activation effect, furthermore, has a cell proliferation inhibitory effect with respect to not only human PIK3CA mutation-positive breast cancer cell lines in which MCT4 is not expressed but also human breast cancer cell lines which do not have mutation of PIK3CA in which MCT4 is not expressed, and exhibits an anti-tumor effect in a human PIK3CA mutation-positive breast cancer cell line MDA-MB-453 cell in a cancer-bearing mouse in which the MCT4 is not expressed, thereby completing the present invention. A bicyclic nitrogen-containing aromatic heterocyclic amide compound of the present invention can be used as an agent for treating breast cancer, in particular, breast cancer in which the MCT4 is not expressed, and among others, PIK3CA mutation-positive breast cancer in which the MCT4 is not expressed.本發明為提供一種作為乳癌治療劑有用之化合物。本發明者們對於具有Complex I阻礙作用及AMPK活化作用之化合物進行檢討，確認本發明的二環式含氮芳香族雜環醯胺化合物為具有良好Complex I阻礙作用及AMPK活化作用，且不僅對不表現MCT4之人類PIK3CA突變陽性乳癌細胞株，且對於沒有MCT4的表現且不具有PIK3CA之突變的人類乳癌細胞株，具有細胞增殖阻礙作用、及對於不表現MCT4之人類PIK3CA突變陽性乳癌細胞株MDA-MB-453細胞罹癌老鼠顯示抗腫瘤作用確認，而完成本發明。本發明的二環式含氮芳香族雜環醯胺化合物可作為乳癌，特別為不表現MCT4之乳癌，尤其可作為不表現MCT4之PIK3CA突變陽性乳癌的治療劑使用。
