Invasive Breast Cancer (IDC/ILC)

Breast cancers that have spread into surrounding breast tissue are known as invasive breast cancers. Most breast cancers are invasive, but there are different types of invasive breast cancer. The two most common types are invasive ductal carcinoma(IDC) and invasive lobular carcinoma (ILC).

Inflammatory breast cancerand triple negative breast cancer are also types of invasive breast cancer.

Invasive (infiltrating) ductal carcinoma (IDC)

This is the most common type of breast cancer. About 8 in 10 invasive breast cancers are invasive (or infiltrating) ductal carcinomas (IDC).

IDC starts in the cells that line a milk duct in the breast. From there, the cancer breaks through the wall of the duct, and grows into the nearby breast tissues. At this point, it may be able to spread (metastasize) to other parts of the body through the lymph system and bloodstream.

Invasive lobular carcinoma (ILC)

About 1 in 10 invasive breast cancers is an invasive lobular carcinoma (ILC).

ILC starts in the breast glands that make milk (lobules). Like IDC, it can spread (metastasize) to other parts of the body. Invasive lobular carcinoma may be harder to detect on physical exam and imaging, like mammograms, than invasive ductal carcinoma. And compared to other kinds of invasive carcinoma, it is more likely to affect both breasts. About 1 in 5 women with ILC might have cancer in both breasts at the time they are diagnosed.

Less common types of invasive breast cancer

There are some special types of breast cancer that are sub-types of invasive carcinoma. They are less common than the breast cancers named above and each typically make up fewer than 5% of all breast cancers. These are often named after features of the cancer cells, like the ways the cells are arranged.

Some of these may have a better prognosis than the more common IDC. These include:

• Adenoid cystic (or adenocystic) carcinoma
• Low-grade adenosquamous carcinoma (this is a type of metaplastic carcinoma)
• Medullary carcinoma
• Mucinous (or colloid) carcinoma
• Papillary carcinoma
• Tubular carcinoma

Some sub-types have the same or maybe worse prognoses than IDC. These include:

• Metaplastic carcinoma (most types, including spindle cell and squamous, except low grade adenosquamous carcinoma)
• Micropapillary carcinoma
• Mixed carcinoma (has features of both invasive ductal and invasive lobular)

In general, all of these sub-types are still treated like IDC.

Treating invasive breast cancer

Treatment of invasive breast cancer depends on how advanced the cancer is (the stage of the cancer) and other factors. Most women will have some type of surgery to remove the tumor. Depending on the type of breast cancer and how advanced it is, you might need other types of treatment as well, either before or after surgery, or sometimes both.

See Treating Breast Cancer for details on different types of treatment, as well as common treatment approaches based on the stage or other factors.