According to [WebMD](http://www.webmd.com/a-to-z-guides/swollen-lymph-nodes-topic-overview) this may be due to melanoma. If my father has an irregular mole on his cheek and back could the swollen lymph nodes be a result of melanoma?
To help you with this, we need much more information. Demographics to begin with and more details about when the swelling started, any other problems, etc. For example right now there's about 15 differentials I can think of off the top of my head that can be causing swollen lymph nodes in the groin area. It can be the most common and benign cause = manscaping/ladyscaping (shaving in the general area) to the melanoma you suggested.