The short answer
Carcinoma in situ means abnormal or cancer cells are contained in the layer where they started and have not grown into nearby tissue. Because these cells have not invaded or spread, in situ findings are often very early and highly treatable.
Carcinoma in situ means abnormal cells are present but have not grown into nearby tissue.
'In situ' is Latin for 'in its original place.'
Because the cells have not invaded, they have not spread to other parts of the body.
In situ findings are often very early and highly treatable.
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The full explanation.
The short version
"Carcinoma in situ" is one of the more technical-looking phrases on a pathology report, but the idea is fairly simple. Carcinoma is a cancer that begins in the cells lining or covering organs and tissues. In situ is Latin for "in its original place." Put together, the phrase means abnormal or cancerous-looking cells that are still contained in the layer where they started and have not grown into nearby tissue.
Why "in situ" matters
The reason this distinction matters so much is spread. Cancer becomes dangerous when it invades surrounding tissue and travels to other parts of the body. In situ cells have not done that. They are confined to their starting layer, so at this stage they have not gained the ability to spread. That is why in situ findings are often described as very early or non-invasive.
Pre-cancer or early cancer?
Depending on the type and location, a care team may describe carcinoma in situ as a pre-cancer or as an early, non-invasive cancer. The label varies, and the wording on your report reflects what the pathologist saw under the microscope. Either way, the shared feature is that the cells have not invaded.
What usually happens next
Because in situ changes have not spread, they are often very treatable. Depending on the situation, your care team may recommend removing the area, watching it closely, or another approach. Not every in situ change would progress to invasive cancer if left alone, but because that is difficult to predict, care teams often treat or monitor them early.
What to ask
Ask your care team what type of carcinoma in situ your report describes, whether they consider it pre-cancer or early cancer in your case, and what your options are. Their reading of your full report is what applies to you.
Words to know
Tap any term to see what it means.
Common questions
Is carcinoma in situ cancer?
It sits at the earliest end of the scale. The cells look cancerous under a microscope but have not grown into nearby tissue, so they have not spread. Some care teams describe it as a very early or non-invasive cancer, and some as a pre-cancer, depending on the type.
Can carcinoma in situ spread?
By definition, in situ cells have not invaded surrounding tissue, so at this stage they have not gained the ability to spread to other parts of the body. That is a key reason it is often treated early or watched closely.
How is carcinoma in situ treated?
Treatment depends on the type and location. Options may include removing the area, monitoring closely, or other approaches. Your care team will recommend what fits your situation.
Will carcinoma in situ turn into invasive cancer?
Not always. Some in situ changes never progress, while others could over time. Because this is hard to predict, care teams often act early or monitor closely.
Questions to ask your doctor
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Your next step
Plain-language definitions for the words on your report.
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