Merck’s Cancer Blockbuster Keytruda Powers Drugmaker’s Profit

Merck & Co.’s blockbuster cancer treatment Keytruda continued to reap rewards as its market domination expanded, leading to strong second-quarter sales and an increase in the drugmaker’s earnings forecast.

Part of a new class of drugs that harness the body’s immune system to attack tumors, Keytruda sold $1.67 billion in the quarter, an increase of nearly 90 percent from the same time a year ago and in line with analysts’ estimates of $1.66 billion.

The drug has become a core element of Merck’s growth, particularly in the large and lucrative area of lung cancer. Earlier this year the drug showed ...