Mary Burrows, who was chief executive of Betsi Cadwaladr health board, moved from Colwyn Bay, Conwy county, to London two months ago.
She is staying with her son while she receives treatment for breast cancer.
"Treatments that have not been approved by Nice are not routinely available in Wales," a health board statement said.
A £200m-a-year cancer drug fund was set up in England in 2011. There is no similar fund in Wales.
Mrs Burrows said her consultant in Wales advised her to go to the Royal Marsden Hospital, Surrey, for the next stage of her treatment because the drug she needed was not available in Wales.
She called the situation "distressing," adding: "A lot of people can't just move their family to another UK nation. There needs to be a debate across all of the UK about how we fund these treatments.
"Not just cancer treatments; advanced technologies and surgeries coming through that people will want to access."
Mrs Burrows left her role with the health board last January.
She said she had "arguments with myself" about the fairness of the Welsh government policy and if having a cancer drug fund takes resources from people with other illnesses.
Mrs Burrows' husband died two years ago of advanced melanoma after he was also unable to get treatment in Wales, she said.
Now she is calling for more investment in the NHS "across the board".
A Betsi Cadwaladr spokeswoman said: "Where a clinician wishes to use a treatment that has not received Nice approval, they can make an application to the health board under the all-Wales individual  patient funding request process.
"These requests are con­sidered by an expert panel. Because each patient is different, each case has to be individu­ally assessed."
A former head of a Welsh health board has moved to England in order to get a cancer drug.