Understanding IDC (Invasive Ductal Carcinoma)

Patient Expert

Breast cancer comes in a variety of types. The most common is invasive (or infiltrating) ductal carcinoma (IDC), cancer of the breast ducts. Find out exactly what IDC is - and what treatments you might expect to have.

What is IDC?

IDC starts with atypical (mutated) cells collecting in a woman's breast ducts, the tiny tubes that carry milk from the breast lobules to the nipple. When these cells break through the duct wall and start moving into the surrounding tissue, they're classified as cancer.

While some breast cancer is difficult to detect, IDC is fairly straightforward: it's characterized by a lump in the breast made up of cancerous cells surrounded by scar tissue caused by the cancer. Surgery to remove the lump usually marks the beginning of a woman's cancer treatment.

Invasive ductal carcinoma is the most common type of breast cancer: about 80 percent of women with invasive breast cancer have IDC. The up side of IDC is that since so many women have it, there's been a lot of research around treatment, with that research leading to steadily improving outcomes.

Why does IDC develop?

If researchers knew why cells suddenly start to move and migrate, they might be able to figure out how to stop them. Right now, their best guess is not that the cells themselves suddenly became more aggressive, but that something around the cells - a hormone, other cells - gives them the "go ahead" to move. But that's still a theory; research continues.


Surgery is usually the first step for women with IDC. The type of surgery depends on a number of factors, including tumor size; whether any other lumps have been detected, and the various ways the pathologist interprets the biopsy sample. A lumpectomy (breast conservation surgery) removes just the lump and some surrounding tissue; a mastectomy removes the entire breast.

Lumpectomy vs. mastectomy

Lumpectomy vs. mastectomy is one of the toughest decisions a woman with breast cancer has to make. Some women, no matter how small the lump, decide they can't stand the thought of cancer in their breast, and would just as soon get rid of the breast than continue to worry about it. Other women prefer the less invasive lumpectomy procedure, trusting and hoping that between that and radiation, the cancer will be killed.

Thankfully, many hospitals and cancer centers offer help with this stressful decision via a "shared decision making" center, where trained professionals help patients weigh the pros and cons of both options.


Radiation to destroy cancer cells near the site of the surgery is usually the next step, if the patient has had a lumpectomy. Typically, mastectomy patients don't require radiation; since the entire breast is gone, there's nothing to irradiate.


When cancer cells travel, the first place they're liable to appear is in lymph nodes, tiny nodes designed to rid the body of foreign elements: bacteria, viruses, cancer, etc. During breast surgery, one or more lymph nodes in the armpit are removed, examined, and labeled positive (cancer cells), or negative (no cancer cells). Even one positive lymph node is a sign that the cancer is starting to advance, and the signal that treatment will probably be more extensive.

If it's discovered that the cancer has spread outside the breast to the underarm lymph nodes or beyond, the patient will most likely undergo chemotherapy. Chemo includes a regimen of powerful drugs delivered over the course of several months; its goal is to kill cancer cells wherever they may have spread in the body.

Hormone therapy

Once active treatment (surgery, radiation, chemotherapy) ends, most women will be put on a course of hormone therapy drugs. These drugs are designed to prevent breast cancer from recurring, and are indicated for survivors whose cancer is hormone-receptive (ER+/PR+).

Hormone-receptive breast cancer relies on female sex hormones, chiefly estrogen, to grow. Deprived of estrogen, the cancer cells will die. Hormone therapy drugs deprive cancer cells of estrogen.

Some of the most common hormone therapy drugs include tamoxifen, and a class of drugs known as aromatase inhibitors: Arimidex, Femara, and Aromasin. These drugs will typically be taken for 5 to 10 years after the end of active treatment.

Though not considered hormone therapy, Herceptin is another drug that helps prevent cancer recurrence. Called a biologic, Herceptin attaches itself to cancer cells and prevents them from receiving growth signals.

See more helpful articles:

Just Diagnosed? We Can Help

A Guide to Breast Cancer Treatment

Chemotherapy Regimens for Breast Cancer

Breast Cancer: Relieving Stress, One Step at a Time

A Guide to Survivorship: Life After Treatment

Breast cancer survivor and award-winning author PJ Hamel, a long-time contributor to the HealthCentral community, counsels women with breast cancer through the volunteer program at her local hospital. She founded and manages a large and active online survivor support network.