Hospital visits among women with skeletal-related events secondary to breast cancer and bone metastases: a nationwide population-based cohort study in Denmark

Figures & data

Table 1 Descriptive characteristics of 569 breast cancer patients with bone metastases and subsequent SREs

Characteristics
Age at primary cancer diagnosis, yearsa	61.7 (52.9–70.7)
Tumor stage at primary cancer diagnosis, n (%)
Local	78 (13.7)
Regional	253 (44.5)
Distant metastases	191 (33.6)
Unknown	47 (8.3)
SRE, n (%)
One SRE	153 (100)
RT	117 (76.5)
PF	19 (12.4)
SSC	14 (9.2)
SB	3 (2.0)
Multiple SREs	416 (100)
Multiple treatments with RT alone	268 (64.4)
RT combined with PF, SSC, and/or SB	119 (28.6)
PF, SCC, and/or SB	29 (7.0)
Months from primary cancer diagnosis to bone metastasesa	12.3 (0.8–29.0)
Months from bone metastases to first SREa	0.8 (0.1–6.0)
Months from first SRE to end of follow-upa	3.0 (2.8–3.2)

Note:

a Median (interquartile range).

Abbreviations: PF, pathological fracture; RT, radiation therapy; SB, surgery to bone; SCC, spinal cord compression; SREs, skeletal-related events.

Figure 1 Hospital visits for women with only one SRE by SRE type.

Abbreviations: RT, radiation therapy; PF, pathological fracture; SCC, spinal cord compression; SRE, skeletal-related event.

Table 2 Hospital visits and follow-up time among 569 breast cancer patients with bone metastases and subsequent SREs

Hospital services	1 SRE (n = 153)			>1 SRE (n = 416)
	Pre-SRE	Diagnostic period	Post-SRE	Pre-SRE	Diagnostic period	Post-SRE
Inpatient visits
Patients, n (%)	79 (51.6)	85 (55.6)	105 (68.6)	226 (54.3)	233 (56.0)	335 (80.5)
Visits	128	96	184	433	271	734
Median (range)	1 (0–1)	1 (0–2)	1 (0–11)	1 (0–12)	1 (0–3)	1 (1–13)
Per 100 person-days (95% CI)	0.9 (0.8–1.1)	4.2 (3.4–5.1)	1.5 (1.3–1.8)	1.2 (1.1–1.3)	4.3 (3.9–4.9)	1.9 (1.8–2.1)
Rate ratioa	1 (ref)	4.5 (3.4–5.9)	1.7 (1.3–2.1)	1 (ref)	3.8 (3.2–4.4)	1.7 (1.5–1.9)
Bed days
Patients, n (%)	79 (51.6)	85 (55.6)	105 (68.6)	226 (54.3)	233 (56.0)	335 (80.5)
Days	1201	742	1690	2415	1706	8757
Median (range)	1 (0–72)	2 (0–15)	5 (0–90)	2 (0–90)	1 (0–15)	13 (0–158)
Per 100 person-days (95% CI)	8.7 (8.2–9.2)	32.3 (30.1–34.7)	14.2 (13.5–14.9)	6.5 (6.2–6.7)	27.3 (26.1–28.7)	23.1 (22.6–23.6)
Rate ratioa	1 (ref)	3.7 (3.4–4.1)	1.6 (1.5–1.8)	1 (ref)	4.2 (4.0–4.5)	3.6 (3.4–3.7)
Emergency room visits
Patients, n (%)	14 (9.2)	16 (10.5)	12 (7.8)	38 (9.1)	39 (9.4)	90 (21.6)
Visits	18	16	14	45	43	110
Median (range)	0 (0–2)	0 (0–1)	0 (0–3)	0 (0–2)	0 (0–2)	0 (0–3)
Per 100 person-days (95% CI)	0.1 (0.1–0.2)	0.7 (0.4–1.1)	0.1 (0.1–0.2)	0.1 (0.1–0.2)	0.7 (0.5–0.9)	0.3 (0.2–0.3)
Rate ratioa	1 (ref)	5.3 (2.5–11.1)	0.9 (0.4–1.9)	1 (ref)	5.7 (3.7–8.9)	2.4 (1.7–3.5)
Outpatient visits
Patients, n (%)	139 (90.8)	109 (71.2)	145 (94.8)	359 (86.3)	325 (78.1)	395 (95.0)
Visits	675	196	760	1847	683	4154
Median (range)	3 (0–30)	1 (0–11)	4 (0–26)	4 (1–34)	1 (1–12)	8 (0–71)
Per 100 person-days (95% CI)	4.9 (4.5–5.3)	8.5 (7.4–9.8)	6.4 (5.9–6.9)	4.9 (4.7–5.2)	10.9 (10.2–11.8)	10.9 (10.6–11.3)
Rate ratioa	1 (ref)	1.7 (1.5–2.0)	1.3 (1.2–1.4)	1 (ref)	2.2 (2.0–2.4)	2.2 (2.1–2.3)
Follow-up time, days	13,770	2295	11,899	37,440	6240	37,948

Note:

a The number of visits or days per person-day with the prediagnostic period as reference and 95% CIs.

Abbreviations: CI, confidence interval; SREs, skeletal-related events.

Table S1 Conversion of TNM classification system to summary staging

Summary staging	TNM
Local	T1–4, N0, M0
	T1–2, N0, Mx
	T1, Nx, M0 or Mx
Regional	T1–4 or Tx, N1–3, M0
Distant	Any T, Any N, M1
Unknown	T2–4 or Tx, Nx, M0 or Mx T3–4 or Tx, N0, Mx T1–4 or Tx, N1–3, Mx T0, N1–3, M0–1 or Mx T0, N0 or Nx, M1

Note: x, variable not specified in the Danish Cancer Registry.

Abbreviation: TNM, tumor, nodes, metastasis.

Table S2 Codes to identify skeletal related events in the DNPR among patients with breast cancer and bone metastases

Pathologic fracture (ICD-10 codes)

M80.0: postmenopausal osteoporosis with pathological fracture

M84.4: fracture of bone in neoplastic disease

M90.7: fracture of bone in neoplastic disease

S12.0–12.9: fracture of neck

S22.0: fracture of thoracic vertebra

S22.1: multiple fractures of thoracic spine

S32.0–S32.8: fracture of lumbar spine and pelvis

S52.5–S52.6: fracture of lower end of radius and/or ulna

S72.0–72.9: fracture of femur

Spinal cord compression (ICD-10 codes)

M43.9: deforming dorsopathy, unspecified

M48.5: collapsed vertebra, not elsewhere classified

M49.5: collapsed vertebra I disease classified elsewhere; metastatic fracture of vertebrae

G95.2: cord compression, unspecified

G95.8: other specified diseases of spinal cord

Surgery to bone (NOMESCO classification of surgical procedure code)

KNxJxx: surgical fracture treatment

Radiation therapy (Danish treatment code)

BWGC1: conventional external radiation therapy

Abbreviations: DNPR, Danish National Patient Registry; ICD-10, 10th revision of the International Classification of Diseases; NOMESCO, Nordic Medicostatistical Committee.