Surgery does not always remove all cancer cells, and whether it can depends on several factors including the type of cancer, its location, how far it has spread, and the surgical technique used. While surgery aims to remove the entire tumor and some surrounding tissue to ensure no cancer cells remain, complete removal is not guaranteed in every case.
One of the most precise surgical methods is Mohs micrographic surgery, especially used for certain skin cancers. This technique involves removing the tumor layer by layer and examining each layer under a microscope during the procedure. The surgeon continues removing tissue only where cancer cells are detected until no cancer remains. This method achieves very high cure rates—up to 99% for some skin cancers—because it thoroughly checks all margins for cancer cells while preserving healthy tissue. However, even with Mohs surgery, the success depends on the cancer type and how well it can be visualized and accessed during surgery.
For other cancers, surgeons remove the tumor with a margin of healthy tissue around it, called the surgical margin, to reduce the chance of leaving cancer cells behind. The tissue removed is then examined by a pathologist to check if the margins are “clear,” meaning no cancer cells are found at the edges. If margins are positive, meaning cancer cells are present at the edge, additional surgery or other treatments may be needed. Achieving clear margins can be challenging in tumors located near critical structures or in areas where removing extra tissue could cause significant harm.
In advanced cancers, especially those that have spread (metastasized) to other organs, surgery alone is rarely sufficient to remove all cancer cells. For example, osteosarcoma that has spread to the lungs requires careful planning to remove all visible tumors, but microscopic cancer cells may remain. Similarly, in colorectal or anal cancers that invade nearby organs or tissues, surgeons strive for “negative margin resection,” but this is not always possible depending on tumor extent and patient health.
Modern cancer treatment often combines surgery with chemotherapy, radiation, immunotherapy, or targeted therapies to address cancer cells that surgery cannot remove. For instance, chemotherapy may shrink tumors before surgery, making complete removal more feasible, or it may be used afterward to kill residual cancer cells. In some cases, surgery is part of a comprehensive treatment plan aimed at long-term remission rather than an outright cure.
In summary, while surgery is a critical and often effective method to remove cancer, it does not always remove all cancer cells. The likelihood of complete removal depends on the cancer type, stage, location, surgical technique, and whether additional therapies are used alongside surgery. Surgeons and oncologists carefully evaluate each case to maximize the chances of removing all cancer cells and achieving the best possible outcome.