I am new to statistics and seem to be getting myself more confused the more I read.

I would like to work out the p value (level of significance 0.05).

I have a group of patients all having an MRI scan. As an example, let us say 50 have a suspicious appearance, and 25 have a non-suspicious appearance.

Upon biopsy, 20 of those with a suspicious appearance have cancer. 5 of those with a non-suspicious appearance have cancer on their biopsy.

I was initially led to believe using the chi-squared test for nominal categorical data may be my best bet. However, I am now reading that it may be worth using the Fisher's exact test as one of my cells has an expected frequency of 5 or less.

Extremely grateful for any help you may be able to give. Hope the above is clear.