Angie Everhart -- Cancer Support from Gena Lee Nolin

Angie Everhart says she's been learning a lot about who her "real friends" are in the wake of her thyroid cancer diagnosis ... and one of those friends is Gena Lee Nolin.

"Anytime you have the big C put in front of you, you do a lot of reflecting on your life," Everhart tells TMZ ... "You learn who your real friends are."

Everhart says one of the first people who reached out was Nolin ... a longtime friend who knows a little something about thyroid issues (she was diagnosed with hyperthyroidism in 2009).

"Sometimes in this town, you don’t know how people will react. My family and those friends who knew about it before it became public, have been wonderful. I am very grateful," Everhart says.