Noa Argamani, 26, was kidnapped from the music festival in southern Israel on October 7 when Hamas militants attacked and killed hundreds.
A video of her abduction, which showed her screaming while seated on the back of a motorcycle behind her captor, circulated on social media in the days after.
On Wednesday, her mother Liora Argamani issued an emotional video message from her apartment in Tel Aviv, near the cancer treatment clinic, according to The Times of Israel.
"I have cancer, brain cancer," a translation of her message says. "I don’t know how much time I have left. I wish for the chance to see my Noa at home."
"Noa," her mother continues. "I want to tell you if I don’t see you, please know we did everything we could to get you released fast.
"The whole world loves you."
Over the last week, a ceasefire in Gaza has allowed for the swap of Israeli hostages and Palestinian detainees.
Since Friday, Hamas has released over 80 hostages, mostly Israeli nationals, while Israel has freed more than 180 Palestinian detainees.
Israel and Hamas agreed on Thursday to extend the temporary ceasefire for another day, with Qatar outlining its terms, just moments before the previous deal was due to expire.
Word of the extension came just as the truce was to expire at 7am (5am GMT) on Thursday.
At least 1,200 people were killed in Israel during Hamas' attack on October 7.
More than 15,000 Palestinians have died since the start of the war, according to the Hamas-run Gaza Health Ministry. The figure includes 6,150 children and 4,000 women.
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