Mrs Zaghari-Ratcliffes family have issued a statement about her condition, saying she had been "complaining of sharp stabbing pains in her breasts" for more than a year.
Breast cancer history
They said she had been given a mammogram by the prisons gynaecologist, which gave an inconclusive result.
After insisting on seeing an outside specialist, the family said Mrs Zaghari-Ratcliffe was then taken to hospital for an ultrasound on Saturday.
They said although the doctor thought the lumps were likely to be benign, he did note her family having a history of breast cancer.
She was given anti-inflammatory medication and vitamin pills and was to be seen by the specialist again next week to see whether there was any improvement or whether she might need surgery, the family said.
The full details of the allegations against Mrs Zaghari-Ratcliffe have never been made fully public.
She maintains the purpose of her trip to Iran was to visit family and for her daughter to meet her grandparents but speaking in Westminster on 1 November, UK Foreign Secretary Boris Johnson appeared to contradict her account when he wrongly said she had been training journalists there.
Four days later, Mrs Zaghari-Ratcliffe was recalled to court in Iran and his remark cited as evidence against her, prompting fears her five-year sentence could be extended.
However, her family say there have been no developments on new charges against her since her court appearance. Her lawyer also says he has not been contacted by the Iranian judiciary.
In the statement her husband, Richard Ratcliffe, describes his earlier phone conversation with Mr Johnson and says the minister is trying to find time to meet him "in the next few days".
t came after Environment Secretary Michael Gove told the BBC he did not know what Mrs Zaghari-Ratcliffe had been doing in Iran when she was arrested.
He later said he would "take her husbands assurance" that she was on holiday.
Amid calls for his resignation over the matter, the foreign secretary earlier this week clarified that the UK government had "no doubt" that a holiday was the sole purpose of her visit to Iran.
Mr Ratcliffe said his wife had been angered by Mr Johnsons initial remarks and Iranian media coverage of her case.
But he restated his belief that it was not in Mrs Zaghari-Ratcliffes interests for anyone to resign.