"TLC has chronicled Bill and Jen's lives since 2009 and at their request, we will be following them through this challenge," a TLC spokesperson tells PEOPLE. "Jen is a doctor and teacher and she saw this as an opportunity to educate and possibly help, through sharing her story."
Arnold, 39, is a neonatologist at Texas Children's Hospital where she serves as medical director of the Pediatric Simulation Center and an assistant professor of pediatrics at Baylor College of Medicine.
She is "currently undergoing treatment, including surgery and chemotherapy," she told PEOPLE Thursday.
Arnold and her husband Bill Klein, 38, allowed fans into their journey to become parents to son Will, 3, and daughter Zoey, 2, whom they recently adopted.
"We allowed our lives to be filmed because we wanted people to understand more about our condition and others who are like us," Klein told PEOPLE earlier this year.
Arnold and Klein both have types of dwarfism, as do their children.
"A little girl came up to me in a store and said, 'You are a little person,' very matter-of-factly and I said, 'Yes, I am, thank you very much,' " Arnold told PEOPLE earlier this year. "We have an opportunity to raise awareness and that's wonderful."
Fans who would like to Tweet well-wishes to the family can do so with this hashtag: #GetWellJen.