Amid a dry spell for breakthrough cancer drugs, recent U.S. approval of Eisai Co.'s Halaven represents some vindication for a small group of researchers who believe, contrary to recent pharmaceutical fashion, that molecules from nature hold promise against hard-to-treat diseases.

The Food and Drug Administration's approval of Halaven in November for treating late-stage breast cancer was a triumph of chemistry and tenacious research. Its path, extending nearly three decades from the first studies, demonstrates not only potential...