Cornish-Bowden stepped down after the International Biotechnology trust, which she chairs, appointed Schroders as the firm's alternative investment fund manager in August, with the move coming into effect today (17 November).
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In a stock exchange notice, Schroders said the Oriental Income's board was now beginning the process finding her replacement.
Paul Meader, chair of the trust, thanked Cornish-Bowden "for her significant contribution as a non-executive director over the past five years".
"We are really sorry to lose her expertise, wisdom and good humour earlier than planned. We wish her well," said.
Cornish-Bowden worked for as a fund manager for 12 years at Morgan Stanley Investment Management, where she was managing director and head of the global equity team.