Table 1.

Characteristics of breast cancer patients with ESR1 mutations (n=28)

	Number of patients with ESR1 mutation	Total number of patients tested	% of patients
ER+	27	217	12.5
PR+	24	177	13.6
ER+ or PR+	27	222	12.1
ER+/HER2	2	30	6.7
Triple negative	1*	119	0.8
Specimen site
Primary breast tumor	0		0.0
Local recurrence	3		10.7
Metastasis	25		89.3

Note:

^*This patient with ER+ primary breast cancer presented with lung metastases and biopsy of one of the lung metastases revealed a triple negative breast cancer.

Abbreviations: ER, estrogen receptor; HER-2, human epidermal growth receptor 2; PR, progesterone receptor.