It is not known when she was diagnosed with the latest ailment.
The cancer revelation came to light in legal documents filed by her husband of 41 years, Artis Mills, who has asked a California judge to grant him control of her finances.
Mills claims the At Last singer is gravely ill and has become too sick to manage her own money.
Her statements have been backed up by Dr. Elaine James, who is of no relation to the star. The medic maintains the ailing legend needs help feeding, dressing and cleaning herself and cannot even sign her own name.
Mills is seeking control of more than $1 million , but is facing a challenge from James' son, Donto, who was handed power of attorney along with his wife Christy and brother Sametto in 2008.
Donto James has submitted his own court declaration, insisting he has no objections to releasing the money to cover the costs of his mother's medical treatment, but would prefer a third party to be placed in charge "to avoid present and future family conflict and discrepancies".
A hearing at a Riverside County court, near James and Mills' home in Woodcrest, is scheduled for Friday.
Etta James has been out of the spotlight since January 2010, when she was hospitalized in Southern California with a serious infection.
At the time, she had been seeking treatment to kick a dependency on painkillers and over-the-counter medication.
James' public battle with heroin addiction and numerous stints in rehab for substance abuse were chronicled in 2008 film Cadillac Records, starring Beyonce Knowles as the R&B icon.