In total, 1462 patients completed baseline interview and enrolled into the study; 1310 (89.6%), 1162 (79.5%) and 1173 (80.2%) participants completed the 18, 36 and 60-months follow-up interviews respectively. Among 1462 enrolled patients, 1019 patients completed all four assessments (T0, T1, T2 and T3) and were included in the present analysis (Figure 1). Those who did not complete all follow-ups were excluded. Patients who completed all follow-ups at the four time-points showed similar baseline characteristics with the whole cohort.
The baseline demographic and clinical characteristics of patients included in this analysis are provided in Table 1. The mean age at diagnosis was 52 years. Sixty-two percent had no comorbidity. Nearly half of the patients (47%) were post-menopausal at diagnosis. Obesity was observed in 28% of patients. Thirty-seven percent belonged to AJCC stage 0-I, 46% stage II and 17% stage III. ER, PR and HER2 positivity were presented in 75%, 59% and 17% of the patients. All patients in this analysis have completed breast cancer surgery. Majority of patients had received adjuvant chemotherapy, radiotherapy and endocrine therapy, with the corresponding figure being 76.0%, 70.8% and 76.3%, respectively. At baseline, only a small group of patients were current smokers or drinkers, at 1.1% and 1.5%, respectively.
Comparison of physical activity between pre- and post-diagnosis
The mean levels of physical activity at T0 (pre-diagnosis), T1, T2 and T3 were 5.9, 9.9, 9.8 and 9,3 MET-hours/week, respectively. The overall level of physical activity at post-diagnosis was significantly higher than that at pre-diagnosis, with mean values of 9.6 vs 5.9 MET-hours/week respectively, P < 0.001 (Table 2). When comparing between T1 and T2, T1 and T3 as well as T2 and T3, there was no significant difference between any two follow-ups at post-diagnosis (P > 0.05, each). The proportions of participants who never did exercise at pre- and post-diagnosis were 46.4% and 10.9%, respectively. However, for those did exercise, the proportions of participants who met the exercise recommendation of WCRF/AICR were relatively low; the figures increased from 20.7% at pre-diagnosis to 35.1% post-diagnosis (P < 0.001).
Change in level of physical activity between pre- and post-diagnosis in individual patient
The changes of physical activity between pre- and post-diagnosis in individual patient are shown in supplementary Table 2. Compared to pre-diagnosis, most of the patients improved or had no change in level of physical activity at post-diagnosis, with the respective proportions being 48.2% and 43.8%, respectively. Only 8.0% of the patients had their level of physical activity declined at post-diagnosis.
In total, 20.7% of patients changed from no or low to high level of physical activity after diagnosis. The proportions patients with such positive change by socio-demographic, clinical and lifestyle factors are presented in Table 3. Univariate analysis showed that patients with the following characteristics are more likely to make such positive changes: patients who were aged≥40 years (compared to those who were aged < 40 years), non-obese (compared to obese), stage II-III (compared to stage 0-I), and having received adjuvant chemotherapy (compared to no chemotherapy).
Multivariate logistic regression model was used to investigate potential characteristics which could predict higher likelihood of such positive changes. The variables entered into the model were those with P < 0.1 in the univariate analysis, which included age at diagnosis, marital status, menopausal status, BMI at diagnosis, AJCC stage and chemotherapy. The results of multivariate analysis are presented in supplementary Table 3. Compared to patients who were aged < 40 years, those who were aged from 40 to 59 years were more likely to make such positive change [age group 40-49 years and 50-59 years: odds ratio (OR) = 2.7, 95%CI: 1.3~5.8, P = 0.008; OR = 3.2, 95%CI: 1.5~7.2, P = 0.004, respectively. Patients who were obese at diagnosis were unlikely to make such change after diagnosis compared to those who were underweight (OR = 0.4, 95%CI: 0.2~1.0, P = 0.042).
Absolute changes of physical activity between pre- and post-diagnosis by socio-demographic, clinical and lifestyle factors
The absolute changes in level of physical activity between pre- and post-diagnosis by socio-demographic, clinical and lifestyle factors were presented in Table 4. Compared to pre-diagnosis, the level of physical activity increased by 2.2 MET-hours/week at post-diagnosis. Univariate analysis showed that higher increase in physical activity was observed among breast cancer patients aged between 40-59 years (compared to those who were aged≥60 years), had a partner (married or cohabitating), not working (compared to full time or part-time) and had no comorbidity (compared to patients who had 1 or more comorbidities).
Multivariate linear regression model was used to investigate the association between absolute changes in level of physical activity and socio-demographic, clinical and lifestyle factors. The variables entered into the model were those with P < 0.1 in the univariate analysis, which included age at diagnosis, marital status, household income, employment status, BMI at diagnosis and number of comorbidities. The results are presented in supplementary Table 4. Compared to patients who had a partner (married or cohabitating), those who were single (unmarried, divorced or widowed) had lower increase in level of physical activity between pre and post-diagnosis (β = -2.0, 95%CI: -3.7~-0.3, P = 0.021). Patients who were not working at baseline showed more increase in level of physical activity after diagnosis compared to those in full-time job (β = 2.7, 95%CI: 0.9~4.5, P = 0.002). Patients with one comorbidity at baseline showed lower increase in level of physical activity after diagnosis compared with those who had no comorbidity (β = -2.8, 95%CI: -4.7~-1.0, P = 0.002).