"Melanoma can metastasize to almost any organ," Alam said. "And then it's not noticed until something happens."
Prior to her diagnosis, Williams had no reason to think anything could go wrong with her body. She was active, running after her two-year-old son, and enjoyed yoga and eating healthfully. She ran a successful photography business. Learning she had cancer, something she said she thought of as an older person's disease, was a shock.
"I didn't realize it could happen to someone so young," Williams said.
But Alam said melanoma is particularly aggressive in young people, striking hard and moving quickly. And while there are a variety of treatment options, there is no reliable therapy when the cancer reaches stage 4.
Williams is undergoing chemotherapy but is exploring a variety of treatment options abroad -- some not approved for use in the U.S. -- if her current treatments stop giving positive results. Right now, Williams said she is focusing on spending time with her husband, son, and friends.
But Williams won't be watching the season finale of Grey's Anatomy tonight.
"I feel a connection [to the character] but it's too new and too fresh," Williams said. "Looking back a year from now and I'm recovered, it might be a different story."
Read more about Naomi Williams at Pictures of Hope.
ABC News' Dan Childs contributed to this report.