A routine blood test may help predict survival in patients with an aggressive form of skin cancer known as Merkel cell carcinoma, according to new findings by Fox Chase Cancer Center researchers. The results will be presented Oct. 31 at the American Society for Radiation Oncology's 54th Annual Meeting.

"With such a fast-growing cancer, we get one question a lot: 'how long do I have?'," says Matthew Johnson, MD, a resident physician in the Department of Radiation Oncology at Fox Chase and lead author on the study. "That's usually hard to answer. These findings enable us to give a more educated response."

Specifically, Johnson and his colleagues found that patients with Merkel cell carcinoma who had low numbers of lymphocytes -- a type of white blood cell that participates in immune function -- didn't live as long after treatment as those with higher lymphocyte counts.

The difference was remarkable. Among people whose absolute lymphocyte count (ALC) was below the cutoff (1500 cells per cubic millimeter of blood, or 1.5 k/mm3), half survived 25 months or less after surgery, chemotherapy, or radiation. Among those with ALCs in the normal range, half lived close to 100 months or more following treatment. Disease-free survival was also much longer in patients with higher ALCs.

"Since ALC has been tied to prognosis in other types of cancer, we were expecting to see some difference between patients with high and low counts," says Johnson. "But it was definitely a bigger difference than what we were anticipating."

Merkel cell carcinoma is a rare and aggressive type of skin cancer, usually striking older people and those with weakened immune systems.

During the study, Johnson and his team reviewed medical records of 64 patients treated for Merkel cell carcinoma between 1992 and 2010 at Fox Chase. All patients had had their blood analyzed the month before surgery, chemotherapy, or radiation.

Approximately two-thirds of patients had a normal ALC. Along with having longer overall survival, these patients were much more likely to be disease-free 60 months later (67%) than those with a low ALC (24%).

ALC may be associated with survival because it's a marker of overall immune health, says Johnson, and healthier immune systems may keep a cancer in check so it doesn't continue to grow.

Doctors routinely check a patient's ALC as part of a standard blood count, says Johnson. They just typically don't know how to interpret those particular results. Since checking a patient's ALC is already routine, it would be "reasonable, based on our conclusions," for a patient to ask his or her doctor for the results of that test, he notes.

However, if a patient's ALC is particularly low, there's little the doctor would do differently to treat Merkel cell carcinoma, since such an aggressive cancer is always treated aggressively. But many patients believe it's helpful to know their prognosis, he says.

"ALC provides patients with some information about how long they may have left. There are a lot of patients who just want to know."

Johnson's co-authors include Aruna Turaka, Fang Zhu, Thomas Galloway, Jeffrey Farma, and Clifford Perlis from Fox Chase.