Pfizer Inc. shares rose 0.7% in heavy Thursday afternoon trade after the company said its therapy for a rare and fatal form of cardiomyopathy met its primary endpoint in a late-stage clinical trial. Compared with the placebo, the therapy, tafamidis, showed a statistically significant reduction in all-cause mortality and frequency of cardiovascular-related hospitalizations at 30 months, the company said. The phase 3 trial, ATTR-ACT, enrolled 441 patients. Transthyretin cardiomyopathy is caused by unstable proteins in the body misfolding, affecting the heart muscle and leading to heart failure. Alynlam Pharmaceuticals Inc. , which is studying its patisiran therapy in hereditary ATTR amyloidosis with cardiomyopathy, had shares fall nearly 7% in extremely heavy trade. Ionis Pharmaceuticals Inc. , which is developing the therapy inotersen for patients with ATTR cardiomyopathy as well, had shares drop 3% in extremely heavy trade. MyoKardia Inc. , which is developing therapies for heritable cardiomyopathies, rose 1.9% in moderate afternoon trade. Pfizer shares have dropped 2.3% month-to-date, compared with a 2.5% drop in the S&P 500 .