NEW YORK - A federal health official’s ruling has cleared the way for 50 types of cancer to be added to the list of sicknesses covered by a $4.3 billion fund set up to compensate and treat people exposed to the toxic smoke, dust, and fumes in the months after the Sept. 11, 2001, terrorist attacks.

The decision, released Friday afternoon, came as a vindication for hundreds and perhaps thousands of people who have asserted - often in the face of resistance from public health officials - that their cancers were caused by their exposure to the dust cloud and debris thrown up in the aftermath of the attack.