"Your cancer is back."
These four words are perhaps the most dreaded that any cancer survivor can hear.
And in less than a week, two prominent figures on the national political scene received this news from their doctors.
Thursday, Elizabeth Edwards, 57, wife of Democratic presidential hopeful John Edwards, announced that the breast cancer she'd been treated for in 2004 had returned, this time in her bone.
And Tuesday, White House press secretary Tony Snow, 51, revealed that his colon cancer, which he was diagnosed with in 2005, had recurred and spread to his liver.
"The news that Tony Snow has suffered a recurrence of colon cancer, coming on the heels of Elizabeth Edwards' announcement last week that her breast cancer has returned, points to why recurrence is such a worrisome issue for cancer patients," said Dr. Harmon Eyre, chief medical officer of the American Cancer Society in a statement Tuesday.
"Cancer recurrence is a very real possibility that patients do need to be aware of."
In his last bout with cancer, Snow had his colon removed and went through a course of chemotherapy. Though the therapy was designed to eliminate the disease, a suspicious growth on his lower pelvis prompted removal and a biopsy early last week, which revealed the disease.
Snow's situation in some ways echoes that of Edwards, whose doctor found evidence of her recurring cancer while taking an X-ray of a fractured rib.
Like many other Americans who experience a cancer recurrence, Snow and Edwards face uncertain odds
Ultimately, the goal of any cancer treatment is to either remove or destroy all the cancer cells in the body. At the end of a successful treatment, a patient is considered to be in remission, which means that no remaining cancer cells can be detected in the body.
But while the first wave of surgery and chemotherapy may remove all evidence of cancer, microscopic cancer cells sometimes survive the treatment and remain undetected in the body. With time, these rogue cells can create new tumors of their own, leading to recurrence.
Depending on the type of cancer, recurrence can happen weeks, months, or even years after treatment of the original cancer.
Adding further mystery to the phenomenon of recurrence is the fact that it is nearly impossible to predict in any given case whether recurrence is likely or not.
"The earlier an initial cancer is caught, the less likely it will recur, but this is not an absolute," said Dr. Leonard Zwelling, vice president of research administration at the University of Texas M.D. Anderson Cancer Center in Houston.
What researchers do know is that when it comes to colon cancer, the liver is the most common site of recurrence, followed by the lung.
If the cancer comes back as a single "hot spot," surgeons will normally try to surgically remove the cancer cells as soon as they are found.
In these cases, the prognosis is generally much better; several clinical trials have revealed that isolated spots of colon cancer in the liver or lungs can be removed surgically and cured about one-quarter of the time.
But while some patients have a single site of cancer, the majority of patients have widespread disease that can't be removed through a single surgery. When this happens, doctors usually resort to chemotherapy to try to control the disease.
In Snow's case, the latter situation seems more likely.
"If the lesion was resectable [removable], I suspect it would have been resected at the time," Dr. James Watson, a surgical oncologist at Fox Chase Cancer Center in Philadelphia, Pa., told Dr. Tim Johnson, ABC News medical editor, on ABC News Now's Healthy Life program Tuesday.
"I suspect there was more than one lesion found."
According to figures from the National Cancer Institute, about half of all colon cancers eventually spread to the liver, either at the time the disease is first detected or as a result of disease recurrence.
So what are the chances that Snow will survive this repeat episode? The exact answer to this question is impossible to determine, as each individual and each case of cancer has a host of different characteristics that affect chances of survival.
But a comprehensive look at all recurrent cancer patients shows that the statistics are not promising.
"If a person develops a spread of colon cancer to the liver, the chances they can be cured by surgery and chemotherapy is between 25 and 40 percent," said Dr. David Schoetz of the Lahey Clinic in Burlington, Mass., and former president of the American Society of Colon and Rectal Surgeons.
"So I would say that Tony Snow is in pretty big trouble."
Watson agreed. "The odds are not in his favor for a 100 percent cure," he said.
Still, Schoetz said, Snow's situation is not hopeless. He added that though it is impossible to reliably predict the chances of survival for either Snow or Edwards, Snow's prognosis may well be better.
"If you had to pick, colon cancer recurrence is probably a little more curable than breast cancer recurrence," Schoetz said.
And Watson said recent advancements in treatment at least give Snow's doctors needed ammunition against the resurgence of his disease.
"We've made enormous strides in colon cancer in the last decade," Watson said. "Certainly a repeat diagnosis of colon cancer can be a blow to the family, but there are still many options."
Whatever the case, however, Watson said that in all likelihood doctors would not be able to completely eliminate Snow's cancer, and he would be put on a continuing chemotherapy regimen to keep the disease in check.
With an arsenal of cancer therapies available to oncologists today -- and treatments offering more hope on the way -- doctors today are able to deal more effectively with recurrent cancer than ever before.
"Most oncologists view colon cancer as more of a chronic disease, especially in patients who have a recurrence," Watson said.
But so far, it is impossible to ensure that a cancer will not resurface once it has gone into remission.
"You can't prevent recurrence from happening," Schoetz said, adding that for the time being, the best way to deal with the possibility of recurrence is to complete all recommended courses of chemotherapy and adhere to regular screening.
"Colon cancer and breast cancer are both extremely common cancers in this country," Schoetz said. "These are both diseases that have pretty intensive screening programs to find precancerous lesions."
This means that annual mammograms and colonoscopies can go a long way in detecting potential problems early -- a crucial step in managing any cancer.