Period of follow-up | Adjusted I* | Adjusted II† | Fully adjusted‡ | |||
Season of surgery | HR (95% CI) | p Value | HR (95% CI) | p Value | HR (95% CI) | p Value |
0–1 years after surgery | ||||||
Winter | 1 (reference) | 0.053 | 1 (reference) | 0.067 | 1 (reference) | 0.052 |
Spring | 1.07 (0.95 to 1.20) | 1.06 (0.95 to 1.19) | 1.07 (0.96 to 1.20) | |||
Summer | 1.09 (0.97 to 1.22) | 1.08 (0.96 to 1.21) | 1.12 (1.00 to 1.25) | |||
Autumn | 0.95 (0.84 to 1.06) | 0.94 (0.84 to 1.06) | 0.97 (0.86 to 1.09) | |||
0–2 years after surgery | ||||||
Winter | 1 (reference) | 0.19 | 1 (reference) | 0.17 | 1 (reference) | 0.43 |
Spring | 0.99 (0.92 to 1.06) | 0.98 (0.92 to 1.06) | 1.00 (0.93 to 1.07) | |||
Summer | 0.99 (0.92 to 1.06) | 0.99 (0.92 to 1.06) | 1.01 (0.94 to 1.08) | |||
Autumn | 0.93 (0.87 to 1.00) | 0.93 (0.86 to 1.00) | 0.96 (0.89 to 1.03) | |||
0–5 years after surgery | ||||||
Winter | 1 (reference) | 0.60 | 1 (reference) | 0.48 | 1 (reference) | 0.96 |
Spring | 0.98 (0.94 to 1.03) | 0.98 (0.94 to 1.03) | 1.00 (0.95 to 1.04) | |||
Summer | 0.98 (0.94 to 1.02) | 0.97 (0.93 to 1.02) | 1.00 (0.95 to 1.04) | |||
Autumn | 0.97 (0.93 to 1.01) | 0.97 (0.93 to 1.01) | 0.99 (0.95 to 1.03) | |||
0–10 years after surgery | ||||||
Winter | 1 (reference) | 0.90 | 1 (reference) | 0.81 | 1 (reference) | 0.92 |
Spring | 1.00 (0.96 to 1.03) | 1.00 (0.96 to 1.03) | 1.01 (0.98 to 1.05) | |||
Summer | 1.00 (0.96 to 1.03) | 0.99 (0.96 to 1.03) | 1.01 (0.98 to 1.05) | |||
Autumn | 0.99 (0.95 to 1.02) | 0.98 (0.95 to 1.02) | 1.00 (0.97 to 1.04) |
Estimates of season of surgery are shown among 79 658 Danish women operated for breast cancer between 1 June 1978 and 31 May 2010.
↵* Model stratified for treatment programme.
↵† Model stratified for treatment programme and age at surgery.
↵‡ Model stratified for treatment programme, age at surgery, hormone receptor status and nodal status and including the effects of tumour size and histological group.