Fig. 3

Interaction between different RS cutoffs and chemotherapy in young and old patients. The size of the point in Figure 3 represents the negative logarithm of interaction P-value. The bigger the point, the less the P-value, which means the higher the statistical significance. Blue points represent the interaction P-value ≥0.05. The red points represent that although the P-value < 0.05, the 95% confidence interval of the hazard ratio for chemotherapy ranges 0 to infinite, due to the few numbers of patients or events. Only the yellow points represent the valid RS thresholds, which have significant interaction with chemotherapy usage. The selection of RS thresholds followed this process: 1) Selecting an age, which has valid RS values (yellow points) both in A and B. 2) Choosing the RS threshold with the highest statistical significance, which is 25 in A and 36 in B (indicated by the arrow)