The Girls Aloud singer is currently awaiting test results from doctors after an operation last week, according to The Sun.
However, doctors are said to have advised Harding that the moles were most likely removed in time with no need for further treatment.
The minor surgery took place at a London hospital last Wednesday (October 17), two days before Girls Aloud announced their comeback tour and greatest hits album Ten.
"This is an incredibly stressful time for her," a friend of Harding is quoted as saying. "It's early days and the doctors are very positive - but the word 'cancer' is terrifying to hear and Sarah is naturally stressing about it."
The insider added that Harding's Girls Aloud bandmates are supporting her, saying: "The girls are completely behind her.
"Some of the fans have suggested she hasn't been enthusiastic about the tour, but the girls have told her not to stress because she'll only run herself down and make herself sick."
Girls Aloud will release their new Children in Need single 'Something New' on November 18, performing the track live for the first time during the fundraiser on November 16.
Watch last week's Girls Aloud press conference below:
Photo gallery - Girls Aloud through the years:
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