THE SHOW MUST NOT GO ON: Sass & Bide designers Heidi Middleton and Sarah-Jane Clarke have cancelled their New York Fashion Week show, which was scheduled for Sept. 6 at 7 p.m. in Bryant Park. The duo decided it would be best for Middleton to sit this show week out so she can recuperate from her on-going chemotherapy treatments. Middleton was diagnosed with breast cancer earlier this year, just 12 days after the birth of her second daughter, Elke Bay. A spokeswoman for Sass & Bide insisted that the designers would be back for the shows in February, but even before that, they would be in New York in November to show their spring collection. "Heidi is doing well," the spokeswoman said. "Her doctors just thought it would be best for her to stay in Australia for now and not travel to New York."