On Tuesday, shares of ImmunoGen Inc. are falling, down over 14% in morning trading after the company proposed a $100 million convertible senior note offering due in 2021.

The notes will be offered by the initial purchasers to qualified institutional buyers only, and in accordance with Rule 144A under the Securities Act of 1933, as amended. ImmunoGen expects the sale to close on June 20, 2016.

The company will also grant initial purchasers of the notes an option to buy up to an additional $15 million aggregate principal amount of the notes on the same terms and conditions to cover any over-allotments. This option is exercisable for 30 days.

In a press release, ImmunoGen said they intend to use the net proceeds of the offering for “its operations, including but not limited to clinical trial expenditures, the manufacture of its experimental therapies, other research and development expenditures, and other corporate purposes, capital expenditures and working capital.”

ImmunoGen develops pharmaceuticals, primarily for the treatment of cancer. The company's product candidates are called tumor-activated prodrugs and are based on its proprietary immunoconjugate technology platform.

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