By 1960, Carson had sufficient research material and the writing was progressing rapidly. She had investigated hundreds of individual incidents of pesticide exposure and the resulting human sickness and ecological damage. In January 1960, she suffered an illness which kept her bedridden for weeks, delaying the book. As she was nearing full recovery in March, she discovered cysts in her left breast, requiring a mastectomy. By December that year, Carson discovered that she had breast cancer, which had metastasized. Her research was also delayed by revision work for a new edition of "The Sea Around Us", and by a collaborative photo essay with Erich Hartmann. Most of the research and writing was done by the fall of 1960, except for a discussion of recent research on biological controls and investigations of some new pesticides. However, further health troubles delayed the final revisions in 1961 and early 1962.