Fianna Fáil TD Mary O'Rourke said she would support her nephew Brian Lenihan for the future leadership of the party if his “health could bear it”.
Mrs O'Rourke revealed that Mr Lenihan has not been receiving treatment for his pancreatic cancer since last summer.
She told 2fm presenter Ryan Tubridy that his radiation and chemotherapy treatments finished in “June or July”. His cancer has “neither developed nor diminished" since then, she added.
Mrs O'Rourke said her nephew's state of health was her “first waking thought” and the reason why she worried about his ability to take the Fianna Fáil leadership in the event of the Taoiseach stepping down.
She called for a special meeting of the party next month where alternatives to Mr Cowen could throw their hats into the ring.
She expressed surprised that a letter she sent to chief whip John Curran calling for such a meeting, which had only been seen by her secretary, was made public.
However, she believed there would be “no merit” in changing the leadership of the party before the budget is passed by the Dáil.
The 73-year-old former minister also revealed that she was interested in standing again in the coming general election but would talk it over with her family at Christmas.
She expressed no interest in standing for the Presidency, saying she would be “appalled by the strictures” of the role.
