By the third grade, Dan Pardi of Norwood, Mass., could say he'd collected more than 100,000 baseball cards. And that he'd survived cancer.
"At 7, you don't know what's going on," said Pardi, who'd been diagnosed with acute lymphoblastic leukemia, one of the most common forms of childhood cancer. "At that age, you think that every kid goes through it."
Now 23, Pardi said his college friends couldn't believe he'd ever had cancer -- and survived. "When I went to college, I told my friends I'd had childhood cancer and people thought, really? You don't look it," said Pardi, who was treated at the Dana Farber Cancer Institute in Boston. "I didn't know there was a look to cancer."
Now, just like Pardi, more people can call themselves cancer survivors. Nearly one in 20 Americans over the age of 20 is a cancer survivor, thanks to advances in early detection and treatment, according to a new analysis by the National Cancer Institute and Centers for Disease Control and Prevention.
"It's really quite staggering, and it's quite wonderful," said Dr. Stephen Edge, medical director of the breast center at Roswell Park Cancer Institute in Buffalo, N.Y.
The CDC defines a cancer survivor as anyone at any age who has ever been diagnosed with any form of cancer and may have undergone treatment during or before 2007. By this criteria, nearly 12 million Americans could call themselves cancer survivors in 2007, up from 10 million survivors in 2001, according to the report. Fifty-four percent of survivors are women, and close to 46 percent are men.
But an increase in the number of cancer survivors does not necessarily mean that there are a higher number of new diagnoses of cancer, said Edge.
"If incidence stays the same and we have better treatment, then of course prevalence would go up," he said. "But that's nothing to worry about. It just means survival for a longer period of time."
Breast, prostate and colorectal cancer are among the most common cancers, accounting for nearly half of all cancer diagnoses. And nearly half of all survivors of every type of cancer were diagnosed with the disease as adults.
Since children are not screened for cancer, the increase in childhood cancer survivorship stems from early treatment and advances in treatment. Today, 75 percent to 80 percent of children with any form of cancer can expect to survive.
"The majority are now surviving, whereas a decade or so ago they didn't," said Linda Jacobs, a registered nurse and director at the Livestrong Survivorship Center of Excellence and Living Well After Cancer program at the the University of Pennsylvania. "That can be said for many cancers at any age, depending on the type."
Survivorship for both adults and children means more than overcoming the cancer itself. Many experts said the surprising number of survivors is a wake-up call to all physicians in every specialty to not only understand their patients' cancer history but also the long-term effects of the disease and the treatment.
"The current thought is oncologists take care of cancer patients," said Dr. Lisa Diller, clinical director of pediatric oncology at Dana Farber Cancer Institute. "But cancer is not a lethal disease anymore, and now maybe the oncologist is no longer the center of a patient's health care."
The chances of cancer reoccurring depend on the form of cancer. Many cancer survivors endure long-term health effects, including infertility, osteoporosis and even post-traumatic stress disorder as a result of some cancer therapies. Some may also experience secondary cancers as a result of some types of treatments.
"These effects manifest themselves unrelated to their cancer," said Diller. "The people who provide primary care in this country will need to know more about how to care wholly for cancer survivors."
Many larger medical centers, especially specialized cancer centers, are doing just that. Messages poured in to ABC News' Medical Unit from more than 25 medical and cancer specialty centers across the nation, describing comprehensive survivorship programs. The programs work with health care providers from various subspecialties who help assess a survivor's medical and mental health needs after treatment.
"It's important to understand the cancer you had and the risk of recurrence or other health concerns," said Diller.
Unlike support groups, many of these programs offer individualized after-treatment plans for survivors. The University of Chicago Medical Center runs a sexual medicine clinic to help women who have survived breast or gynecological cancer regain their sexual independence.
Cedars-Sinai Medical Center in Los Angeles conducts a program that helps survivors overcome "chemobrain," a term used to describe adjustment disorders, and cognitive and learning disabilities, which can be side effects of extensive chemotherapy.
"I think there is hope for many. Despite diagnosis, people are surviving because of treatment options and supportive and follow-up care," said Jacobs.
Pardi said he was surprised to hear the number of survivors was so high -- especially since he recalled that his aunt, who had lung cancer, did not survive -- but was glad to hear there were more like him.
"Ever since I've been in remission, I haven't felt like cancer is a part of my life," said Pardi, who said he continues to receive routine screenings and annual follow-up care for his childhood leukemia.
Pardi said he'd kept his baseball cards and, with help from his oncologist, traded in the cancer.
"I really think the real definition of cancer survivor," said Pardi, "is someone who can almost 100 percent put the cancer behind them and move on to live just as full a life."