Carcinoma in situ is an early form of carcinoma that has not moved into surrounding tissues. It does not typically form a tumor, although there are a few exceptions to this. This type of carcinoma typically grows in a flat patch or along the curve of the body where it is located. While carcinoma in situ itself is not invasive or malignant, if left untreated, it can develop into an invasive form of carcinoma. Most doctors refer to it as a pre-cancer, and want to remove the lesion before it has a chance to develop into a malignant form of carcinoma.
Some of the different forms of carcinoma in situ include bladder and cervical cancers, ductal carcinoma in situ, which is a form of breast cancer, colon polyps, and Bowen's disease, which is carcinoma of the skin. The only form considered deadly is bronchioloalveolar carcinoma. This condition develops in the lung, eventually expanding to fill the lung, making it impossible to breathe. Bronchioloalveolar carcinoma is malignant, so its classification in this group of carcinomas is controversial.
One common form of carcinoma in situ is Bowen's disease. Bowen's disease is an early form of squamous cell carcinoma. Bowen's disease is more common in women than men, and can develop anywhere on the body. It is triggered by sun damage, immune suppression, viral infections, or because of skin injury. Bowen's disease begins as an enlarged area with an irregular border, and, left alone, may become malignant. A physician removes the plaque in one of several ways; with local chemotherapy, freezing it using cryotherapy, or surgically.
Some forms of carcinoma in situ do develop into tumors if left untreated. Colon polyps and some forms of breast cancer are both examples of malignant tumors that begin as carcinoma in situ. Regardless of whether the carcinoma is located in a spot where it is likely to develop into a tumor or not, it is important that it be removed as quickly as possible.
Carcinoma in situ is not malignant or invasive, so there are no stray cancerous cells outside of the area of carcinoma. This means that removing the carcinoma will eliminate the risk of cancer. The method of removal depends on where the carcinoma is located. Doctors remove some carcinomas, such as colon polyps nonsurgically with an endoscope. Others require surgical removal, and still others are removed with a laser.