Merck (MRK) and Pfizer (PFE) are leading pharmaceutical companies with strong product and pipeline portfolios in oncology. Both companies also have presences in vaccines, neuroscience, and immunology.However. oncology accounts for more than 50% of Merck’s total revenues. Blockbuster PD-L1 inhibitor, Keytruda, approved for several types of cancers, alone accounts for around 50% of its pharmaceutical sales.As regards Pfizer, oncology sales comprise around 25% of its total revenues. Its position in oncology wa ...