Table 5.
Differences in Demographic and Clinical Characteristics Between the Higher Energy (n=127) and Lower Energy (n=270) Classes
| Characteristic | Higher Energy Class n=127 (31.9%) Mean (SD) |
Lower Energy Class n=270 (67.8%) Mean (SD) |
Statistic and p-value |
|---|---|---|---|
| Age (years) | 56.5 (10.8) | 54.2 (11.8) | t=1.88, p=.061 |
| Education (years) | 15.7 (2.2) | 15.7 (2.8) | t=0.01, p=.994 |
| Karnofsky Performance Status score | 95.4 (9.4) | 92.2 (10.6) | t=3.06, p=.002 |
| Self-administered Comorbidity Questionnaire score | 3.6 (2.3) | 4.6 (3.0) | t=−3.47, p=.001 |
| Mean energy score at enrollment | 6.1 (2.7) | 4.4 (2.2) | t=−6.26, p<.0001 |
| Number of breast biopsies in past year | 1.5 (0.8) | 1.5 (0.8) | U, p=.604 |
| Number of positive lymph nodes | 0.8 (2.0) | 1.0 (2.3) | t=0.76, p=.450 |
| Number of lymph nodes removed | 5.0 (6.3) | 6.1 (6.9) | t=−1.51, p=.132 |
| n (%) | n (%) | ||
| Ethnicity White Black Asian/Pacific Islander Hispanic/Mixed ethnic background/Other |
86 (68.3) 10 (7.9) 16 (12.7) 14 (11.1) |
169 (62.8) 30 (11.2) 33 (12.3) 37 (13.8) |
Χ2=1.75, p=.627 |
| Married/partnered (% yes) | 50 (39.7) | 114 (42.7) | FE, p=.5 86 |
| Work for pay (% yes) | 66 (52.4) | 123 (45.9) | FE, p=.236 |
| Lives alone (% yes) | 29 (23.0) | 65 (24.4) | FE, p=.801 |
| Gone through menopause (% yes) | 84 (68.3) | 163 (62.0) | FE, p=.2 56 |
| Stage of disease 0 I IIA and IIB IIIA, IIIB, IIIC, and IV |
29 (22.8) 51 (40.2) 39 (30.7) 8 (6.3) |
44 (16.3) 100 (37.0) 101 (37.4) 25 (9.3) |
U, p=.040a |
| Surgical treatment Breast conservation Mastectomy |
100 (78.7) 27 (21.3) |
218 (80.7) 52 (19.3) |
FE, p=.686 |
| Sentinel node biopsy (% yes) | 103 (81.1) | 224 (83.0) | FE, p=.673 |
| Axillary lymph node dissection (% yes) | 40 (31.7) | 108 (40.0) | FE, p= .12 0 |
| Breast reconstruction at the time of surgery (% yes) | 28 (22.2) | 58 (21.5) | FE, p=.896 |
| Neoadjuvant chemotherapy (% yes) | 22 (17.5) | 57 (21.1) | FE, p=.421 |
| Radiation therapy during the first 6 months (% yes) | 75 (59.1) | 149 (55.2) | FE, p=.515 |
| Chemotherapy during the first 6 months (% yes) | 34 (26.8) | 99 (36.7) | FE, p=.054 |
Abbreviations: FE = Fisher Exact test, SD = standard deviation, U=Mann Whitney U test
a
Post-hoc contrasts of the difference in stage of disease between the Higher Energy and Lower Energy classes failed to identify the sub-groups who differed between the classes (p<.0083).