LONDON (Reuters) - Kate, Britain's Princess of Wales, is due to make her first public appearance on Saturday since surgery five months ago revealed the presence of cancer, saying she was making good progress through treatment but was "not out of the woods".

Kate has undergone preventative chemotherapy since the cancer announcement, and while treatment is ongoing, her improved health means she will be able to appear in public for the first time since last December.

She is set to accompany her three children in a carriage during "Trooping the Colour", an annual military parade held in central London to mark the monarch's official birthday.

She will also join King Charles, Queen Camilla and the other senior family members on the balcony of Buckingham Palace, the high-profile pinnacle of the event.

Kate spent two weeks in hospital in January after she underwent major abdominal surgery, and two months later she announced in a video message that tests had revealed the presence of cancer, and she would begin preventative chemotherapy.

In a message on Friday, she said she had been "blown away" by the thousands of kind messages from across the globe, which had made a world of difference to her and her husband, heir-to-the-throne Prince William.

"I am making good progress, but as anyone going through chemotherapy will know, there are good days and bad days," her statement said.

"I'm looking forward to attending The King's Birthday Parade this weekend with my family and hope to join a few public engagements over the summer, but equally knowing I am not out of the woods yet."

Her office, Kensington Palace, has declined to give any details about the type of cancer or about her treatment, other than to say the preventative chemotherapy had begun in February.

Her illness has coincided with that of Charles, 75, who has also been undergoing treatment for cancer. He returned to public duties in April, and has remained busy, although his diary commitments are being limited to minimise risks to his recovery.

A Buckingham Palace spokesperson said Charles was "delighted" that Kate would be in attendance on Saturday.

(Writing by Alistair Smout; Editing by Sandra Maler)

By Michael Holden