Certain Deferred Stock Units of ImmunoGen, Inc. are subject to a Lock-Up Agreement Ending on 3-JAN-2018. These Deferred Stock Units will be under lockup for 90 days starting from 5-OCT-2017 to 3-JAN-2018. Details: The directors and officers have agreed that they will not offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase or otherwise transfer or dispose of, directly or indirectly, any shares of common stock or any securities convertible into or exercisable or exchangeable for shares of common stock, for a period of 90 days after the date of the final prospectus supplement without the prior written consent of Jefferies LLC and Leerink Partners LLC.