How can i tell if my model is overfitting from the distribution of predicted probabilities?
Such a plot doesn't really tell you much about overfitting.
First, check that your calibration has worked well; it's possible that an incorrect calibration has pushed the probabilities to the extremes.  Otherwise, the distribution of probabilities being so extreme suggests the data just naturally separates into a segment of easy-to-detect cancers and the rest.  Among the latter, it looks like you get reasonably good but not great rank-ordering of cases.