New research by the American Cancer Society (ACS) reveals that, over decades, pancreatic cancer death rates in the US rise and fall along racial lines, going in opposite direction between white and black Americans.

While the data, collected between 1970 and 2009, reveals differences in the way pancreatic cancer has affected white and black men and women over time, the researchers report that the rising and falling cancer rates are largely unexplainable by known risk factors.

The researchers found that in white men, pancreatic cancer death rates decreased by 0.7 percent each year from 1970 to 1995, then reversed, increasing by 0.4 percent per year through 2009, which was the last year data was available.

"Among white women, rates increased slightly from 1970 to 1984, stabilized until the late 1990s, then increased by 0.5 percent per year through 2009," the ACS wrote in a news release. "In contrast, death rates among African Americans increased between 1970 and the late 1980s (women) or early 1990s (men), after which they began to decrease. However, death rates continued to be substantially higher in blacks than in whites in both men and women."

Pancreatic cancer is among the most deadly cancer types; it is the fourth leading cause of death in the US, killing more than 38,000 people in 2013 alone.

Deaths from pancreatic cancer have been increasing over recent years, despite an overall drop in mortality rates for other types of cancer, the ACS said.

The major causes of pancreatic cancer are still not thoroughly understood, but cigarette smoking has been linked to the disease. The prevalence of smoking has decreased in both white and black American men and women since 1965, the ACS said.

"This study underscores the need for urgent action on several fronts," said Ahmedin Jemal, DVM PhD, senior author of the research paper published in the Journal of the National Cancer Institute. "We need to invest more into pancreatic cancer research to understand why this disease is rising or falling in different races. In the meantime, we have to address modifiable risk factors such as obesity and smoking to reduce the future burden of pancreatic cancer in all populations."