What Does Stage 0 Cancer Mean?

Seeing "stage 0" on a report can be confusing, because it sounds like cancer but also like "the very beginning." In most cases, stage 0 means abnormal or cancer cells are present but have not spread into nearby tissue. The cells are still contained where they started.

Stage 0 is often written as "in situ," which is Latin for "in its original place." It describes cells that look abnormal or cancerous under a microscope but have not grown beyond the layer where they began. NCI describes stage 0 as abnormal cells that have not spread to nearby tissue.

Cancer stages describe how much cancer is in the body and whether it has spread. Stage 0 sits at the start of that scale. For stages I to III, NCI says higher numbers mean larger tumors or more spread into nearby tissue. Stage IV means the cancer has spread to distant parts of the body.

NCI gives stage 0 a medical name: carcinoma in situ, or CIS. Then it says something that catches most people off guard. CIS is not cancer, but it may become cancer.

That one line is the heart of the answer. The cells look abnormal under a microscope. But they are still held inside the structure where they started. Stage 0 cells have not spread to nearby tissue.

The best known stage 0 finding is ductal carcinoma in situ of the breast, usually shortened to DCIS.

NCI describes it as abnormal cells in the lining of the milk ducts that have not broken out into other breast tissue. It is equally clear about what it is. DCIS is not cancer. It may be called precancer, because it can spread beyond the ducts and become invasive cancer.

It is more common than most people realize. About 20% to 25% of new breast cancer cases in the United States each year are DCIS. Other names for the same thing are noninvasive breast cancer, intraductal carcinoma, and stage 0 breast cancer.

Most of it is found by screening, not by symptoms. NCI says DCIS usually causes none. Most cases turn up on a routine mammogram. On the image it often shows as breast calcifications, which are white specks in the tissue. Now and then it causes a lump or nipple discharge.

The outlook matches the stage. More than 98% of people diagnosed with DCIS are alive 5 years later. DCIS is also less likely to come back than invasive breast cancer.

NCI answers this in one sentence. DCIS is treated like cancer because doctors do not know which cases will become invasive and spread.

Treatment removes a possibility, not a certainty. NCI says DCIS is almost always treated with surgery. That is usually a lumpectomy. A mastectomy is considered if the DCIS is large, or found in several areas. After a lumpectomy, radiation to the rest of the breast tissue is usual. After a mastectomy it may not be needed. Hormone therapy may be added when the DCIS has hormone receptors.

That is why a diagnosis that sounds mild can still come with a real treatment plan.

For DCIS, NCI reports an excellent outlook, and treatment options include surgery, radiation, and hormone therapy. For other types, ask your care team about the options for your location. NCI notes that doctors do not know which DCIS cases will become invasive, which is why they are treated.

One word matters more than the size of the finding. Does the report say in situ, or invasive?

Cancer registries use a matching set of words for the same idea. NCI lists them: in situ, localized, regional, distant, and unknown. In situ is the first rung.

It is worth reading that line yourself and asking your team to confirm it.

Because "stage 0" covers different situations depending on the type of cancer, the most useful step is to ask your care team:

• What does my specific result mean?
• Is it considered pre-cancer or early cancer?
• What are my options?

Their explanation, based on your full report, is the one that applies to you.

Our guide to cancer staging covers the wider system. Biopsy: How Cancer Is Confirmed covers what to establish first.

• National Cancer Institute — Cancer Staging
• National Cancer Institute — Ductal Carcinoma In Situ (DCIS)