by Jason Wasserman MD PhD FRCPC
April 5, 2026
Adenocarcinoma is a type of cancer that starts in glandular cells — specialized cells that normally produce substances like mucus, hormones, or digestive juices. Glandular cells line the inside of many organs throughout the body, which is why adenocarcinoma is one of the most common types of cancer overall. When you see this word in your pathology report, it tells you the type of cell the cancer came from, not where it is located.
Where does adenocarcinoma develop?
Adenocarcinoma can develop in any organ that contains glandular cells. The most common sites include the colon and rectum, lungs, breast, stomach, pancreas, prostate, and uterus (endometrium). The location matters for treatment planning, so your pathology report will usually name both the cell type (adenocarcinoma) and the organ where the cancer was found — for example, “adenocarcinoma of the colon” or “lung adenocarcinoma.”
What does adenocarcinoma look like under the microscope?
When a pathologist examines adenocarcinoma under the microscope, the cancer cells often still try to form gland-like structures — small tube or ring-shaped arrangements that resemble the glands found in normal tissue. This gland-forming pattern is a key feature that identifies the cancer as an adenocarcinoma rather than another type.
In some cases, the cancer cells have changed so much that they no longer form recognizable glands. When this happens, the tumour is described as poorly differentiated or undifferentiated — terms that mean the cells look very different from the normal tissue they came from. Tumors that still closely resemble normal glandular tissue are described as well differentiated.
What does the grade mean?
Grade describes how abnormal the cancer cells look compared to normal glandular cells. Pathologists assign a grade based largely on how much of the tumour still forms recognizable glands. The grade gives doctors an idea of how quickly the cancer is likely to grow and how it may behave.
- Well differentiated (low grade) — the cancer cells closely resemble normal glandular cells and still form gland-like structures. These tumors tend to grow more slowly.
- Moderately differentiated (intermediate grade) — the cells show more abnormalities but still retain some glandular features.
- Poorly differentiated (high grade) — the cells look very abnormal and form few or no recognizable glands. These tumors tend to grow more quickly and behave more aggressively.
- Undifferentiated (high grade) — the cells bear almost no resemblance to normal glandular tissue. This is the most aggressive grade.
It is worth noting that grading systems vary by cancer type. The criteria used to grade a lung adenocarcinoma, for example, differ from those used for colon or breast adenocarcinoma. Your pathology report will describe the grade specific to your tumour type.
What does adenocarcinoma mean for my diagnosis?
Finding the word adenocarcinoma in your pathology report means that a cancer made up of glandular cells has been identified. It is a diagnosis of cancer — but it is a starting point, not the full picture. The organ where the cancer started, the grade, the stage, and the results of any additional tests will all shape your treatment plan and outlook.
In many organs, adenocarcinoma is the most common type of cancer. This means there is often a well-established understanding of how to treat it, and your oncologist will be familiar with the options available for your specific cancer type and stage.
If you have questions about what your specific adenocarcinoma diagnosis means for your care, the links below are a good place to start. Each diagnosis guide covers a specific type of adenocarcinoma in much greater detail.
Questions to ask your doctor
- What organ did my adenocarcinoma start in, and what grade is it?
- Has the cancer spread beyond where it started, and if so, where?
- What additional tests are being performed, and what information will they provide?
- What treatment options are recommended for my type and grade of adenocarcinoma?
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