The diagnosis took Michael Strahan by surprise.

On Thursday morning, the “Good Morning America” anchor revealed that he had “no idea” that 19-year-old daughter Isabella’s headaches would result in a diagnosis of brain cancer.

“I didn’t notice anything was off until probably September, like October 1,” said Isabella, who initially thought she had vertigo. “That’s when I definitely noticed headaches, nausea, couldn’t walk straight.”

Doctors told Isabella that she had developed a fast-growing 4-centimeter tumor – larger than a golf ball – in the back of her brain, according to the interview. Isabella is now undergoing treatment.

“I’m feeling good, not too bad,” Isabella said. “I’m very excited for this whole process to wrap, but you just have to keep living every day, I think, through the whole thing.”

What is medulloblastoma?

Isabella is among the about 300 to 500 people in the United States who are diagnosed with medulloblastoma each year.

“It’s the most common brain tumor in kids, although it’s still very rare,” said Dr. William Dahut, chief scientific officer for the American Cancer Society. “It can be a very aggressive tumor initially. It can spread to other parts of the brain but doesn’t tend to spread outside of the brain.”

Medulloblastoma can happen at any age, but it most often occurs in children and is well-known as a childhood brain cancer.

“Medulloblastoma is the most common malignant brain tumor in childhood. It is a cancer that arises in the cerebellum, or back part of the brain that controls balance and coordination,” said Dr. Sarah Leary, attending physician and medical director of the Pediatric Brain Tumor Program at Seattle Children’s.

“For a practice like ours, which is a pediatric brain tumor center, these are some of the most common tumors we see,” Leary said, adding that the average age at which medulloblastoma patients are diagnosed is 8.

“But it spans all the way from infants into even older adults, rarely. And so 19 is not particularly rare,” she said of Isabella’s age.

What are medulloblastoma symptoms?

Common symptoms of medulloblastoma like Isabella had – including nausea, vomiting, headaches and loss of balance – easily can be mistaken for symptoms of other types of health conditions, said Leary, who is also a professor at the University of Washington School of Medicine.

“Most symptoms of brain tumors are more common with something else – like most headaches are not a brain tumor. Most vertigo is not a brain tumor. Most nausea is not a brain tumor,” she said.

“What I tell people about the importance of diagnosing a brain tumor, it’s really the follow-up for common symptoms that ends up being the most important,” she said. “If it doesn’t go away like a normal illness or normal symptom would, then you’ve got to keep looking.”

Another symptom associated with medulloblastoma can be hydrocephalus, a neurological disorder caused by excess fluid in the brain.

“The location of the tumor can block the normal flow of cerebrospinal fluid in the brain, which can present as a life-threatening emergency called hydrocephalus, which means ‘water on the brain,’” Leary said. “Hydrocephalus is a medical emergency that requires urgent neurosurgical intervention to relieve the pressure on the brain.”

How is medulloblastoma treated?

Medulloblastoma is typically treated with surgery, radiation and chemotherapy. Sometimes, patients have the opportunity to participate in clinical trials involving stem cell transplants or other emerging therapies.

“When you’re looking at that tumor, you’re also thinking about the fact that fluid may build up on top of the brain – so sometimes you have to remove some of that excess fluid and then you also want to actually do an operation to take out the tumor,” said CNN’s chief medical correspondent Dr. Sanjay Gupta, a brain surgeon who has removed tumors like this in patients.

“What you have to assume with these types of tumors, because they’re malignant, is that no matter how much of the tumor you’ve removed during the operation that there may still be some tumor that’s remaining, and that’s why radiation is often given, which is something Isabella’s already received, and she will be getting chemotherapy as well,” Gupta said. “So, it’s an aggressive tumor, requiring aggressive treatment.”

Isabella said that she underwent surgery on October 27, the day before her 19th birthday, and then several rounds of radiation treatment. She is scheduled to start chemotherapy next month at Duke Children’s Hospital & Health Center in Durham, North Carolina.

“One of the first components is surgery. It’s important in medulloblastoma to remove the tumor as much as possible from the brain, but we know that’s not enough, and so additional treatments are needed. That includes chemotherapy and, in most patients, radiation therapy as well,” said Dr. John Prensner, an assistant professor and expert on pediatric brain cancers at the University of Michigan Chad Carr Pediatric Brain Tumor Center and C.S. Mott Children’s Hospital.

“In some cases, the radiation therapy is not performed if it’s a very young child, where the long-term effects on the developing brain might be too high,” he said. “But in an older individual, that would be a commonly included treatment.”

These treatment approaches can be intense on the body and may last months, leading to side effects such as hair loss, weight loss and upset stomach.

Because of this, Prensner and his colleagues at the University of Michigan have been studying ways in which medulloblastoma treatments can be personalized for patients, based on the biological and genetic factors of the type of disease they have.

“Medulloblastoma is a type of cancer that includes a number of different varieties. You can think about this like when you go to the grocery store and you say, ‘I want to buy an apple,’ but then you show up and you see there’s a number of different types of apples that you could actually buy. Medulloblastoma is similar to that,” Prensner said.

Some types of medulloblastoma may be more aggressive than others, while “in other types of medulloblastoma, cure rates are extremely good,” Prensner said. If a patient is found to have a type that is more easily curable, based on the tumor’s biological and genetic factors, they might be able to receive lower doses of certain treatments.

“You might still achieve the same ability to cure patients without giving quite as many side effects,” Prensner said of the more targeted treatment approaches that are being studied.

“In some cases, historically, we may have given more than is needed, and so you want to give the right amount of treatment for the patient. There’s not necessarily a need to give more than that,” he said. “In the more aggressive forms of medulloblastoma, however, cure rates are still inadequate, and there is a great deal of research happening to identify additional treatments or more effective treatments for these patients.”

What is the prognosis for medulloblastoma?

About 72% of people with medulloblastoma survive at least five years after diagnosis, according to the National Cancer Institute. But many factors can affect that prognosis.

“With early diagnosis, staging with high-quality MRI and immediate treatment that is tailored to individual factors – including stage of disease as well as molecular testing to determine exactly the right type of medulloblastoma – survival will be as high as 80%,” Leary said.

“It is very important to have proper staging and diagnosis, consultation with a center of expertise in medulloblastoma,” she said. “This is a completelly different disease from more common adult brain tumors.”