Jan 8 (Reuters) - Cellectar Biosciences said on Monday that its therapy for a rare form of blood cancer met the main goal in a late-stage study, sending shares up 45% in premarket trading.

In the study, 75.6% of the patients with Waldenstrom's macroglobulinemia (WM) saw cancer decrease in size or disappear after treatment with Cellectar's therapy - Iopofosine.

WM is characterized by an excess of abnormal white blood cells in the bone marrow and is often hard to detect as the symptoms can take years to appear.

The condition impacts approximately 1 in 3.4 million men in the United States and roughly half that number of women in the country.

(Reporting by Christy Santhosh; Editing by Shounak Dasgupta and Tasim Zahid)