A paper by Sebastian Salas-Vega and Elias Mossialos attempts to answer this question looking at nine countries (Australia, Canada, France, Germany, Italy, Japan, Sweden, the United Kingdom, and the United States) using data between 2004 and 2014. They find that:
All nine countries—most notably France and Japan—witnessed an improvement in neoplasm-related years of potential life lost, which suggests that although the costs of drugs have risen, their therapeutic benefits have increased as well. Net economic value derived from cancer drug expenditures appears to have remained positive, with base-case analyses indicating that the United States obtained an estimated $32.6 billion in net positive return from cancer drug care in 2014.
Although cancer drugs are expensive, their value in terms of extending life has been enormous. A 2015 study found that reduction in cancer mortality were largest in the countries that increased spending the most. Specifically:
…the countries that increased spending the most had a 17 percent decrease in amenable mortality, compared to 8 percent in the countries with the lowest growth in cancer spending.