Our knowledge of cancer biology in 2019 is extensive, however there are several enduring problems that make it difficult to translate this knowledge into new, effective therapeutics.

Oncogenes are genes that contribute to tumor initiation and/or tumor progression, and with oncogenes the therapeutic strategy is to block or inhibit their function; we have been fairly successful at this using small molecule drugs and biologics like therapeutic antibodies. On the other hand, tumor suppressor proteins inhibit the development or progression of cancer, and with tumor suppressor genes the therapeutic strategy is to restore or enhance their activity. This has proven to be much more difficult for a variety of reasons. Here, researchers from Harvard discovered that a small molecule already in use as a health supplement restores function of a major tumor suppressor gene called PTEN.
NYT
Science