Table 1.

Clinicopathological Features of Metastatic Breast Cancer Patients Analyzed in This Study According to ESR1 Mutation Status

		Total	Plasma ESR1 Mutation		P
			Positive	Negative
Number		54	13	41
Age at blood sampling (years)	Mean (range)	56.5 (30-74)	56 (35-66)	57 (30-74)	.348*
Estrogen receptor	Positive	54	13	41
	Negative	0	0	0
Progesterone receptor	Positive	40	9	31	.572†
	Negative	11	3	8
	Unknown	3	1	2
HER2 status	Positive	5	0	5	.321†
	Negative	49	13	36
Primary or recurrent	Primary	5	1	4	1.000†
	Recurrent	49	12	37
DFI of recurrent breast cancer (month)	Median (range)	42.8 (1.9-223.5)	52.3 (12.7-177.1)	35.6 (1.9-223.5)	.140*
AI treatment	No AI	7	1	6	.045†
	Adjuvant AI only	11	0	11
	AI for MBC	36	12	24
Duration (month) of AI for MBC	Median (range)	5.6 (0.0-74.8)	30.2 (0.0-74.8)	2.9 (0.0-35.6)	<.001*

HER2, human epidermal receptor 2; DFI, disease-free interval; AI, aromatase inhibitor; MBC, metastatic breast cancer.

^*Mann-Whitney U test.

^†Fisher's exact test.