How can I overlay two ggplot2 objects from contsurvplot package?

I have two plots that are generated from the plot_surv_at_t from the constsurvplot package. One is looking at the 5-year recurrence free survival versus tumor size. The other is cancer specific survival versus tumor size.

model1 <- coxph(Surv(Time_To_Recurrence,Recurrence) ~ Tumor_Size, data = data, x=TRUE)
model2 <- coxph(Surv(CSS,Cancer_Death) ~ Tumor_Size, data = data, x=TRUE)

plot_surv_at_t(time = "Time_To_Recurrence",
               status = "Recurrence", 
               variable = "Tumor_Size",
               data = data1, 
               model = model1, 
               t=60)

plot_surv_at_t(time = "CSS",
               status = "Cancer_Death", 
               variable = "Tumor_Size",
               data = data1, 
               model = model2, 
               t=60)

Each individual plot looks great, but I want to show the impact of size on recurrence free and cancer specific survival in the same plot. I've tried the patchwork package and am able to get them next to each other, but I have not been able to onlay them.

Thanks

Solution

One potential option is to pull the data from the second ggplot2 object and add it to the first ggplot2 object, e.g.

library(survival)
library(survminer)
#> Loading required package: ggplot2
#> Loading required package: ggpubr
#> 
#> Attaching package: 'survminer'
#> The following object is masked from 'package:survival':
#> 
#>     myeloma
#options(timeout = 6000)
#install.packages("contsurvplot", dependencies = TRUE)
library(contsurvplot)

fit <- coxph(Surv(time, status) ~ age, data = lung, x = TRUE)
plot1 <- plot_surv_at_t(time = "time",
               status = "status", 
               variable = "age",
               data = lung, 
               model = fit, 
               t=60)

plot1


lung2 <- lung %>%
  mutate(CSS = sample(1:1000, 228))
fit2 <- coxph(Surv(CSS, status) ~ age, data = lung2, x = TRUE)
plot2 <- plot_surv_at_t(time = "CSS",
                        status = "status", 
                        variable = "age",
                        data = lung2, 
                        model = fit2,
                        t=60)
plot2


plot1 +
  geom_line(data = plot2$data,
            aes(x = cont, y = est),
            color = "red")

^{Created on 2023-03-19 with reprex v2.0.2}