What It Means When Cancer Is 'In Situ' And Why It's The Most Curable
A cancer diagnosis often comes with overwhelming emotions and a flood of unfamiliar medical terms that can spark even more fear. But understanding these terms can help you feel more in control of your health. One term you might hear is "in situ." This means that the cancerous cells are still located in the exact place where they first developed. In other words, they haven't spread to nearby tissue or other parts of the body.
This is generally considered good news. Cancers found in situ are often highly treatable and may even be removed completely, usually through surgery. In medical terms, this is classified as stage 0 cancer. You might also hear it called noninvasive or preinvasive cancer. (Find out the truth behind common myths about food and cancer risk.)
In situ cancers can be considered "curable" because you won't need further treatment for the cancer. According to the American Cancer Society, doctors prefer to say the cancer is "in remission" rather than cured because there's no guarantee that a cancer can't return.
Catching cancer at this early stage is one of the key benefits of regular screening, especially for cancers of the breast, colon, and skin. These cancers often start in situ, and finding them early gives you the best chance for successful treatment.
In situ cancers are often detected through screening
Up to 25% of breast cancer diagnoses are ductal carcinoma in situ (DCIS), according to the Breast Cancer Research Foundation. Although DCIS may increase the risk of developing more invasive breast cancer, it isn't considered life-threatening. These cancerous cells start and usually stay in the milk ducts and rarely spread to the surrounding breast tissue. People with DCIS often don't feel a lump, which is why this type of cancer is typically detected through a mammogram and confirmed with a biopsy of the suspicious tissue. The tumor is usually removed through a lumpectomy to preserve the surrounding breast tissue, and in some cases, radiation therapy is recommended to target any remaining cancerous cells.
Most skin cancer diagnoses are either basal cell carcinoma or squamous cell carcinoma, but the rarer and more dangerous melanoma can also be found in situ. Depending on your overall health and the location of your melanoma in situ, surgery is often the first line of treatment. For people who aren't good candidates for surgery, a cream called imiquimod may be used. This treatment works by stimulating your immune system to fight the cancer (per Cancer Research UK).
Colon cancer often doesn't cause noticeable symptoms until it reaches later stages, according to the Moffitt Cancer Center. That's why regular screening, such as a colonoscopy, is so important for early detection. If your colon cancer is found in situ, the abnormal cells are limited to the innermost layer of the colon wall. These cells can usually be removed during a colonoscopy using a surgical scope, preventing the cancer from progressing.
Why in situ cancers still require serious attention
Even if you're diagnosed with an in situ cancer, it doesn't mean it should be taken lightly. The Breast Cancer Research Foundation reports that up to 50% of untreated ductal carcinoma in situ (DCIS) cases can develop into more invasive breast cancer. The good news is that people who receive treatment for DCIS have a 98% survival rate after 10 years.
An in situ skin carcinoma means the abnormal cells are confined to the upper layers of the skin. But without treatment, these cancers can still become dangerous. Melanoma, for example, can be life-threatening if left untreated because it spreads quickly throughout the body. According to Westlake Dermatology, untreated melanoma can be fatal in as little as four weeks. It's also important to take squamous cell carcinoma seriously. While squamous cell cancers don't tend to spread as quickly as melanoma, they can still be fatal if ignored.
Colon cancer typically grows more slowly than other types of cancer. A polyp found in your colon can take up to 10 years to develop into cancer (per Cleveland Clinic). But that doesn't mean you should delay your colon cancer screening. The National Cancer Institute estimates that more than 154,000 people in the U.S. will be diagnosed with colorectal cancer in 2025, making it the fourth most common cancer behind breast, prostate, and lung cancer. It's also expected to be the second leading cause of cancer-related deaths, behind lung cancer.