The Principal Investigator

The latest data on cancer among African Americans carries a message of hope and concern. Though African American death rates are down across all cancer types, a new report finds the population continues to be diagnosed with late-staged cancers more frequently and have lower survival rates compared to whites.

The findings, released today (2.18.09) are part of the American Cancer Society’s Cancer Facts & Figures for African Americans 2009-2010, a report published every two years.

The report finds the death rates of African American men have decreased faster than those of white men, which the authors attribute to “rapid declines in the death rates from prostate and lung cancers” among African American men. Though African American women have also demonstrated marked decreases in cancer death rates in recent years, slower declines in breast cancer and colorectal cancer death rates has kept their death rates from dropping below those of white women.

The report predicts that, in 2009, roughly 150,090 new cases of cancer will be diagnosed in African Americans, and experts report nearly 63,360 African Americans will die from cancer.

“African Americans have the highest rate of any racial and ethnic group in the U.S. for most cancers,” American Cancer Society chief medical officer Otis W. Brawley said in a news release. “The causes of these disparities are complex and likely reflect social and economic disparities, not biological differences.” Income, access to healthcare and education disparities may all contribute to African Americans seeking out care after cancer has become more invasive and more deadly.

“While it is discouraging that these differences still exist, we absolutely must face them and continue to enact policies to address them in order to save lives and reduce suffering from cancer among African Americans,” Brawley said.

Related links:

Racial gap in cancer deaths as wide as in 1981 (USA TODAY, 2.18.09)

Blacks still dying more of cancer than whites (Scientific American, 2.18.09)

To emerge unscathed after being blasted with radiation, cancer stem cells take advantage of a molecular pathway used to protect normal adult stem cells, according to a report published Wednesday (2.4.09) in Nature.

Scientists at Stanford University and the City of Hope National Medical Center used a combination of information collected from human and mouse breast cancer cells to help them solve the mystery of how cancer stem cells survive the radiation therapy that kills off non-stem cells present in a tumor. The radiation resistance of cancer stem cells allows a tumor to grow back and patients to relapse months to years after therapy.

“Since cancer stem cells appear to be responsible for driving and maintaining tumor growth in many tumors, it is critical to understand the mechanisms by which these cells resist commonly used therapies such as chemotherapy and radiotherapy,” said Stanford radiation oncologist Maximilian Diehn in a press release. “Ultimately, we hope to improve patient outcomes by developing therapeutic approaches that directly target stem cells or that overcome resistance mechanisms.”

Compared to non-stem cells, previous studies found blood and central nervous system stem cells have lower numbers of reactive oxygen species (ROS) that are critical to cell function. Although ROS are naturally produced free radicals, the body has a system in place to keep the chemicals in check throughout the lifetime. Like bouncers at a club, antioxidants help prevent cellular destruction and clean up the messes made by ROS. The breakdown of the antioxidant defense system and subsequent rise of free radicals causes DNA damage and gives rise to a host of diseases, including heart and neurodegenerative disorders.

Radiation therapy tries to take advantage of the wrath free radicals play on a cell by directly ionizing the DNA and intracellular chemicals of cancer cells. Grasping for stability, the reactive intracellular chemicals can tear a cell apart.

To find out what causes cancer stem cells to be more resistant to radiation than other cancer cells, the Stanford team analyzed breast cancer stem cells plucked from human and mouse breast tumors and discoverer the cells had lower levels of pro-oxidant, or free-radical-promoting chemicals compared to normal breast cancer cells.

The scientists then exposed breast cancer stem cells to ionizing radiation and found they underwent less DNA strand breaks compared to the mature breast cells, and populations of breast cancer stem cells were twice as likely to survive in comparison to mature breast cells after exposure to radiation, suggestive of resistance to radiotherapy.

Lastly, when comparing the gene expression in cancer stem cells versus non-stem cells the group uncovered the answer they were looking for: cancer stem cells displayed higher expression levels in genes involved in the production of glutathione (GSH), an antioxidant that deactivates ROS. By blocking GSH, the scientists were able to increase the vulnerability of breast cancer stem cells to radiation.

“Although your body would normally eliminate cells with chromosomal damage, it also needs to spares those cells responsible for regenerating and maintaining the surrounding tissue – the stem cells,” Stanford cancer biologist Michael Clarke said in a press release. “It’s protective.”

Scientists hope to use the information gained from their recent studies can be used to determine ways to “inactive [the] protective mechanism in cancer cells while sparing normal cells,” Clarke said.

Source of cancer stem cells’ resistance to radiation discovered at Stanford [press release]