Hello

I am new to R, and I already need some help. So bear with me.

My research is about predicting response of treatment in patients with pancreatic cancer using cancer biomarkers. For each biomarker, I have created a ROC curve using the pROC package to see have well the biomarker performance (sensitivity, specificity etc.)

```
library(pROC)
d$resb <- ifelse(d$Resectability=="Resectable",1,0)
r.CA199 <- roc(d$resb,d$CA19.9)
coords(r.CA199,
"best",
best.method = "youden",
ret = c("npv", "ppv", "sensitivity", "specificity","threshold"))
plot(r.CA199)
r.VICM <- roc(d$resb,d$VICM)
coords(r.VICM,
"best",
best.method = "youden",
ret = c("npv", "ppv", "sensitivity", "specificity","threshold"))
plot(r.VICM)
```

However, I want to combine the ROC curves of two biomarkers, to see how well they perform together.

My question is: How do I combine the two ROC curves (CA199 and VICM) into one single ROC curve in one plot?

It is my first post, so if you need more information just tell me.

Thank you!