Table 3. Multivariate Cox model (DFS) including interaction of adjuvant chemotherapy and grouping of the risk score.

Usage of chemotherapy	Factorsa	P	HR (95% CI)
General	Chemo. (no vs. yes)	0.075	0.932 (0.119–3.325)
	Grouping (low-risk vs. high-risk)	<0.001	5.338 (2.699–10.558)
	Interaction, Chemo*Grouping	0.078	1.843 (0.933–3.642)
Paclitaxel-based	Chemo. (no vs. yes)	0.011	3.124 (1.536–6.354)
	Grouping (low-risk vs. high-risk)	<0.001	2.410 (1.326–4.379)
	Interaction, Chemo*Grouping	0.002	3.532 (1.577–7.913)

Abbreviations: Chemo, chemotherapy

NOTE: Multivariate analysis of interaction was conducted in two steps. In the first step, the Cox regression model included established prognostic factors (age, menopausal status, lymph node status, tumor size, histological grade, ER, PR, HER2, grouping of the risk score) but not chemotherapy. The first step demonstrated that tumor size (P = 0.004), lymph node status (P = 0.002), PR (P = 0.035), and grouping of the risk score (P < 0.001) were significant independent factors for DFS. Menopausal status (P = 0.070) and histological grade trended (P = 0.078) towards significance. In the second step, interactions between usage of chemotherapy (general or paclitaxel-based) and grouping of the risk score were investigated along with adjustments for those factors (with P < 0.10) identified in the first step. This table shows the results of the second step.

^aHere, we present only three items: usage of chemotherapy, grouping of the risk score and the interaction between them. Other parameters (tumor size, lymph node status, PR status, menopausal status and histological grade) are not shown.