Table 1 Clinicopathological variables in metastatic breast cancer patients at baseline

Age, median (range)

65 (40–90)

65 (45–82)

 < 50

65

48

10

50

 ≥ 50

71

52

10

50

Baseline ECOG

0

75

57

16

90

1

36

27

1

5

2

21

16

1

5

Missing

4

2

PT NHG

I-II

68

62

10

71

III

42

38

4

29

Missing

26

6

PT tumor size

1

49

38

8

44

2

46

36

5

28

3

17

13

3

17

4

17

13

2

11

Missing

7

2

PT node status

negative

39

33

5

28

positive

79

67

13

72

missing

18

2

Breast cancer subtype

ER + HER2-

94

71

11

61

HER2 + 

15

11

5

28

ER- HER2-

24

18

2

11

Missing

3

2

Metastasis-free interval (years)

0

28

21

3

15

 > 0–3

25

18

3

15

 ≥ 3

83

61

14

70

Missing

0

0

Metastatic sites, number

 < 3

96

71

13

65

 ≥ 3

40

29

7

35

Missing

0

0

Site of metastasis

Non-Visceral

56

41

9

45

Visceral

80

59

11

55

Missing

0

0

1st line of treatment for MBC

Endocrine

55

43

3

19

Chemotherapy

60

47

11

69

HER2-targeted

13

10

2

12

Missing

8

4

CTC

 < 5

65

49

8

44

 ≥ 5

69

51

10

56

Missing

2

2

One or more CTC clusters

No

108

81

14

78

Yes

26

19

4

22

Missing

2

2