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."

The party won 33 seats on Thanet District Council, Kent, in May, making it the first authority in the UK to have a UKIP majority.
UKIP councillor Jeff Elenor announced on Tuesday he was defecting to join the Democratic Independent Group.
He joins four other UKIP councillors who defected last month saying they were unhappy with the council's lack of action over Manston Airport.
They also said they were unhappy about what they felt was insufficient focus by the council on issues such as housing, mental health and disabilities.
Mr Elenor said he did not feel the council was fulfilling its election pledge on Manston.
In May, UKIP won 33 seats, the Conservatives 18, Labour four, and independents one - 29 seats were needed for a majority.
UKIP now has 28 members, but remains the largest party on the council.
Earlier this week, the US company seeking to purchase and reopen Manston Airport accused the council leader of holding up the process.
The airport closed in May 2014 and was sold to a private consortium that plans to build homes on the site.
RiverOak said it had offered the money to help with a compulsory purchase order (CPO), and in an email to the council leader, it accused Chris Wells of "throwing one road block after another in front of us in order for you to carry out whatever your real agenda might be".
"Whatever it is, that agenda does not appear to recognise the will of your constituents, which is that Manston Airport be opened and operating at the earliest possible moment," chief investment officer George Yerall said.
Mr Wells said the council was seeking further assurances that RiverOak could afford to purchase the site.
The matter is due to be formally discussed at a cabinet meeting later this month.

Norma Diffley, who ran a boutique in Donaghadee, died in the accident on the A2 dual carriageway between Bangor and Holywood close to the Devil's Elbow at Carney Hill on Monday afternoon.
The 33-year-old man is being questioned on suspicion of dangerous driving causing death.
He was arrested on Tuesday.

It came as a surge in commodity prices saw Brent crude oil rise above $40 a barrel for the first time this year.
The Dow Jones closed up 67.18 points at 17,073.95, while the broader S&P 500 rose 1.77 points to 2,001.76.
However, the tech-heavy Nasdaq index fared less well, falling 8.77 points to 4,708.25.
Oil firms led the Dow higher, with Chevron adding 3.1% and Exxon gaining 2.6%.
A former head of a Welsh health board has moved to England in order to get a cancer drug.
[NEXT_CONCEPT]
The UK Independence Party has lost overall control of its only council.
[NEXT_CONCEPT]
A 33-year-old man has been arrested in connection with a two-vehicle crash which claimed the life of a 75-year-old woman in County Down.
[NEXT_CONCEPT]
(Close): Wall Street's Dow Jones and S&P 500 indexes closed higher for the fifth day running, in their longest winning streak since last October.