Advancements in detection and treatment mean more Americans are surviving cancer than ever before. But as the population of cancer survivors continues to grow at a rapid pace, so do their unmet medical and psychological needs, according to a new report from the American Cancer Society.

Currently, there are more than 15.5 million Americans with a history of cancer living in the U.S. That number is expected reach more than 20 million a decade from now, according to the study, published today in CA: A Cancer Journal for Clinicians, a journal of the American Cancer Society.

"These findings are really important because they're essential for the public health community, advocacy groups, and policy makers to have an understanding of the current and future cancer survivors and their needs in order to best serve them," study author Kim Miller, an epidemiologist at the American Cancer Society, told CBS News. "Many survivors cope with long-term physical, psychological, and socio-economic effects."

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In the study, the term "cancer survivor" refers to a person with a history of cancer, from diagnosis through the remainder of life. It includes both patients receiving treatment and those who have become cancer-free.

According to the report, about one-third of survivors in the U.S. today were diagnosed less than five years ago and more than a half were diagnosed within the past 10 years. Almost half are 70 or older, although patient ages vary by cancer type.

"The population of cancer survivors is increasing at a rapid rate and the fastest growing segment is older cancer survivors and those living more than five years past their diagnosis," study co-author Kevin Stein, Ph.D., vice president of the Behavioral Research Center for the American Cancer Society, said. "So these are long-term cancer survivors who are five, 10, 15, 20 years passed their original diagnosis."

Yet, the very treatment that is saving these patients' lives can also cause additional medical complications, some of which do not occur until years after the completion of treatment. These problems -- referred to by the medical community as "late effects" -- include osteoporosis, neuropathy, organ dysfunction, cognitive issues, and damage to the heart, to name a few.

"The challenge is that the treatments are always changing," Stein said, "so as the treatments change and become more advanced, the late effects change so we're always trying to play catch up."

People who were treated with certain chemotherapy regimens 20 years ago, for example, may have different late effects than people who are treated now with more targeted therapies.

"We're always sort of behind the curve in trying to understand the prevalence and impact of these late effects, how to identify these late effects, and how to either prevent them and manage them," Stein said.

Longer-term physical and psychological problems also plague many patients starting from diagnosis, through treatment, and after treatment is complete. "Those can be things like anxiety, depression, fear that their cancer will return, fatigue, and pain," Stein said.

The authors say they hope their data will encourage future research that will enable physicians to better serve the unique needs of these patients.

"We need to better understand the impacts of the treatments given to cancer patients on their medical and psychological functioning and be able to identify individuals who are at risk for developing these problems and then try to intervene early on to prevent or mitigate symptoms as they appear," Stein said.

The American Cancer Society offers resources for people with a history of cancer and their families on its website, as well as an online community of cancer survivors, called the Cancer Survivors Network.