An international panel of doctors has decided that a type of tumor that was classified as a cancer is not a cancer at all.

As a result, they have officially downgraded the condition, and thousands of patients will be spared removal of their thyroid, treatment with radioactive iodine and regular checkups for the rest of their lives, all to protect against a tumor that was never a threat.

Their conclusion, and the data that led to it, was reported Thursday in the journal JAMA Oncology. The change is expected to affect about 10,000 of the nearly 65,000 thyroid cancer patients a year in the United States. It may also offer grist to those who have been arguing for the reclassification of some other forms of cancer, including certain lesions in the breast and prostate.

The reclassified tumor is a small lump in the thyroid that is completely surrounded by a capsule of fibrous tissue. Its nucleus looks like a cancer but the cells have not broken out of their capsule, and surgery to remove the entire thyroid followed by treatment with radioactive iodine is unnecessary and harmful, the panel said. They have now renamed the tumor. Instead of calling it “encapsulated follicular variant of papillary thyroid carcinoma,” they now call it “noninvasive follicular thyroid neoplasm with papillary-like nuclear features,” or NIFTP. The word “carcinoma” is gone.