Question: A 70-year-old woman presented at our hospital with appetite loss and self-awareness of a mass palpable in her right breast. The family history was unremarkable, and physical examination and mammography revealed a mass lesion in the right breast measuring approximately 2.3 cm in diameter, which was diagnosed pathologically as invasive lobular carcinoma. Laboratory findings showed elevated levels of tumor markers, such as carcinoembryonic antigen (204.4 ng/mL; normal, <3.4), cancer antigen 19-9 (188.6 U/mL; normal, <37), breast cancer antigen 225 (361 U/mL; normal, <160), and National Cancer Center-ST-439 (2770 U/mL; normal, <4.5).