What is stage 0 cancer? Here’s what you should know about this unusual diagnosis.

While most of us have heard of stage I, II, and III cancer—and especially the grimmest stage IV—many people don’t know there’s also an earlier stage of cancer known as stage 0.

Until recently, that included Tina Knowles, the mother of singer Beyonce, who revealed a breast cancer diagnosis in her new memoir. In an interview about the importance of getting screened early and often for cancer she said, “I didn’t know that there was a stage 0. I could have caught this at stage 0 if I had not missed my mammogram.”  

(When should you get screened for breast cancer—and how often?)

It’s unsurprising that Knowles didn’t know about stage 0 as it isn’t as commonly diagnosed as the other stages of cancer. It also isn’t detectable for many types of cancer and often goes by a different name.

Here’s what stage 0 cancer is, what sets it apart from other stages of cancer, and why regular cancer screenings are probably the only way you’re going to catch it.

How many stages of cancer are there?

There are typically thought to be four main stages of cancer. Though sometimes determining these stages can be more complex, they are most often settled on by the TNM (Tumor, Nodes, and Metastasis) staging system—a diagnostic method oncologists follow to identify the size and location of a tumor and how far cancer cells have spread throughout the body.

Stage I of most types of cancer means a malignant (cancerous) growth of cells (known as a tumor) has been identified but is still small and confined to the organ where it originated.

This stage also means that, while those cells are invasive within that organ, they have not spread to any lymph nodes, explains Hatem Soliman, a breast oncologist at the Moffitt Cancer Center in Tampa, Florida. This is important because lymph nodes are found at more than 800 convergences of major blood vessels around the body—cancer identified in any of them means it had to spread from its original location to get there.

Stage II cancer means the primary tumor is large enough to meet sizing criteria that varies by cancer type. It usually also means cancer cells have been discovered in nearby lymph nodes.

(Our bodies are unique. Our cancers are too.)

Stage III cancer is more advanced because it means the primary tumor has grown beyond stage II sizing criteria and that cancer cells are spreading to more lymph nodes.

Stage IV cancer is often called metastatic cancer and means the tumor has grown further still and that the cancer has spread to many more lymph nodes and other parts of the body—often including invading vital organs, explains Elena Ratner, a physician and gynecologic oncologist at Yale Cancer Center in Connecticut. This pervasive spread makes it much harder to contain or eradicate the disease. 

How is stage 0 cancer different? 

Stage 0 cancer is different from these other stages because it means abnormal cells have been identified somewhere in the body, but those cells may not yet be cancerous. And, unlike cancer cells in stage I, they’re not invading even the surrounding tissue of the organ where they originated.

These abnormal cells are also usually too small to form a tumor, so they generally cannot be picked up on internal organ scans like an ultrasound or MRI. They can be discovered on external tissue, however, and are frequently identified in breast tissue, thanks to routine mammograms.

Stage 0 cancer is also sometimes called carcinoma in situ because “in situ” is Latin for “in place.” Sometimes a prefix is also attached to indicate where the worrisome cells are located—such as adenocarcinoma in situ, which refers to affected cell glands in the cervix, lungs, or gastrointestinal tract. 

What is stage 0 breast cancer, or DCIS?

When discovered in breast tissue, stage 0 cancer is diagnosed as ductal carcinoma in situ, or DCIS, with “ductal” referring to the milk ducts in the breasts.

(What are dense breasts? How this common condition complicates cancer detection.)

DCIS “only becomes stage I, II, III, or IV cancer when it bursts through the milk ducts and starts spreading,” says Mehra Golshan, deputy chief medical officer for surgical services at Yale Cancer Center and Smilow Cancer Hospital in Connecticut.

That doesn’t always happen though. “Not all stage 0 breast cancer becomes invasive,” he says, “but over time, some do.”  

Why early cancer diagnosis matters

Because stage 0 cancer can evolve unexpectedly—sometimes months or even years after the abnormal cells are first discovered—patients “need to be followed closely to determine that this area doesn’t develop into cancer,” says Syma Iqbal, a physician and gastrointestinal oncologist at USC Norris Comprehensive Cancer Center in Los Angeles.

Sometimes doctors and patents decide not to wait to see though, she says, and choose to target the abnormal cells with localized radiation or surgical interventions. 

While preventive treatments like these are not ideal, they are greatly preferred over cancer that isn’t discovered until it has spread and is wreaking havoc on multiple organs and systems throughout the body—requiring more invasive treatments like chemotherapy.

This is why the American Cancer Society recommends for women to get screened for cervical cancer beginning at age 25 and for breast cancer starting between ages 40 and 45. The organization also suggests colorectal cancer screening for everyone beginning at age 45; for some men to get screened for prostate cancer at age 45; and for people who smoke or those with a family history of cancer to consider getting checked even sooner. 

When caught and treated because of early screening, “stage 0 breast cancer has a survival rate approaching 99 percent,” says Golshan.

Ratner agrees. “Both doctors and patients get very lucky if the cancer is caught in stage 0 as it is much easier to cure,” she says. “It is the most favorable stage of cancer by far and has the best prognosis.”