How many programs should I aim to apply for PGY2?

I'm currently looking into programs for PGY2 Oncology. I'm a current resident at a large AMC that is an NCI-designated cancer center. Took me some time to figure out what my interest truly is so I opted out from early committing. My current interest is Oncology with a focus on Heme/Onc. I know that I want to continue my training at a large AMC, ideally NCI-designated cancer center. That said, I was wondering what's a good number of programs should I apply to for this upcoming application cycle? I'm pretty geographically bound and only have 4 programs on my list so far. Should I consider to apply to more programs or 4 is a good number for PGY2 application?