NEW YORK (CBSNewYork) — A doctor who arrived with Joan Rivers‘ entourage to her routine throat procedure performed an unplanned biopsy on the comedian just before she went into cardiac arrest last month, a medical source told the New York Daily News.

Rivers’ own doctor performed the biopsy Aug. 28 after another doctor at Yorkville Endoscopy noticed “something” on Rivers’ vocal cords, the source, who is said to have been briefed on the case, told the newspaper.

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The report says the comedian’s vocal cords seized, a condition called laryngospasm, and cut off her air supply. The 81-year-old TV star was then rushed to Mount Sinai Hospital, where she died a week later.

Medical experts told the Daily News the biopsy is not supposed to be performed outside a hosptial.

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“If she had been in a hospital when it happened, she might have been OK,” the source said.

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Rivers’ personal doctor — who identified himself as an ear, nose and throat physician — asked to use Yorkville Endoscopy’s instruments, and was allowed to perform the biopsy, according to the report.

“He asked and they let him,” the source told the newspaper. “A huge no-no.”

Rivers arrived at the Upper East Side clinic to undergo a routine endoscopy.

An autopsy performed by the medical examiner was inconclusive, and more tests are being done to determine the cause of Rivers’ death.

State health officials are investigating the matter, though there is no criminal investigation of the clinic.

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