Cancer is a class of diseases or disorders characterized by the uncontrolled division of cells and the spread of these abnormal cells to other tissues.
X-ray of Ben's spine. ("Every Man for Himself")
This was revealed in "The Cost of Living" to belong to Ben, who said that he wanted Jack to operate on him. Though it was not stated whether it was a malignant or benign tumor, Ben implied that he would not have much time to live if something was not done.
- Jack eventually told Ben that it was malignant.
Later, Jack agreed to operate on Ben, in exchange for Kate and Sawyer being set free. He eventually removed the tumor, though the stitches later became infected. It is not yet known whether Ben returned to full health following the deal Jack made with him, which commuted Juliet's sentence so she would not be executed.
Rachel Carlson during her chemo treatment. ("One of Us")
When Juliet was on the Island, Ben told her that the cancer had returned, but Jacob could heal Rachel if Juliet stayed on the Island to help the pregnant women. When Ben got cancer later, Juliet thought that Ben was lying and that Rachel was dead, but he proved to her that she was alive by showing her a live feed of Rachel with her son. ("One of Us")
- Rose was diagnosed with cancer prior to coming to the Island. It was deemed untreatable at that point, and her husband Bernard took her to a spiritual healer. Miraculously, upon arrival to the Island, the disease underwent spontaneous remission.
- Diane Janssen had a terminal illness and was being treated for it.
- Angelo Busoni had a terminal tumor that Jack unsuccessfully operated on. ("The Hunting Party")
- While being examined because of headaches, Sawyer told Jack that his uncle died of a brain tumor. ("Deus Ex Machina")
- Peter Thompson was diagnosed with inoperable lung and pancreatic cancer after a lifetime of smoking.
- The Alvar Hanso Cancer Center in Geneva, Switzerland was also mentioned.
- A tie-in novel with Lost, entitled Endangered Species, talked about Gayle Harrington (sister of Faith Harrington) who died of cancer.