Understanding ILC (Invasive Lobular Cancer)

Patient Expert

What is ILC?

ILC - invasive (or infiltrating) lobular carcinoma - is similar to IDC (invasive ductal carcinoma), the most common form of breast cancer. The main difference involves geography: IDC occurs in your breast's ducts, the tiny tubes that carry milk from where it's manufactured ­ (in the lobules) to your nipple. ILC occurs in those milk-manufacturing lobules.

Here's what's going on: atypical cells - cells that, for an unknown reason, mutated as they grew - collect in the lobules of a woman's breast. At some point, these cells can break through the lobule wall, and start moving into the surrounding tissue. When this happens, these previously atypical cells become cancer cells.

While 86 percent of all breast cancers occur in the ducts, just 12% occur in the lobules.

How is ILC identified?

Lack of a palpable lump is one aspect of lobular cancer that distinguishes it from ductal. When ductal cancer becomes invasive, it breaks through the duct walls and wreaks havoc in the surrounding breast tissue, creating all kinds of scar tissue; this scar tissue quickly becomes a hard lump, something that can be felt.

In ILC, however, the cancer cells are sneakier. Rather than break out in large groups, they tend to form long, skinny "fingers," which are much less irritating to healthy tissue. Many women with ILC never feel a lump. The only indication cancer is present is a general texture change - a kind of thickening - in the affected part of the breast.

Obviously, since this kind of change is not nearly as straightforward as a lump, it's tougher to notice. The average ductal carcinoma is 2cm by the time it can be felt; the average lobular, 5cm.


ILC treatment is very similar to treatment for IDC. But one difference is typically in the surgery. Because ILC forms long chains of cancer, rather than a lump, it's usually more spread out, and thus more difficult to remove surgically.

For patients having a lumpectomy, it's tougher than usual to get "clean margins" - a margin of healthy breast tissue, all around the tumor(s), that tells the surgeon there's a good chance s/he's cut out all the cancer. Two or even three surgeries may be required for clean margins; and sometimes, even after multiple surgeries, a mastectomy is necessary.


For patients who've undergone a lumpectomy, the next step is typically radiation. By irradiating the tissue closest to the location of the tumor, the radiation oncologist hopes to eradicate any and all stray cancer cells.


If cancer cells have left the breast and are discovered in the underarm lymph nodes, chances are the patient will undergo chemotherapy, a series of drug treatments given over the course of several months. If the spread is minimal, though, the patient may be given the option of skipping chemo - which leads to a tough decision: Have chemo, and endure all of its miserable side effects, some of them potentially permanent? Or skip chemo, and increase the risk of cancer coming back?

Women having to make this difficult chemo decision are often offered the Oncotype DX test, which is a fairly reliable indicator of whether or not chemo will be effective.

Hormone therapy

If a woman's cancer is hormone-receptive - i.e., it requires female sex hormones to grow - her oncologist will typically recommend 5 to 10 years of hormone therapy - a daily pill that helps prevent cancer recurrence by depriving cancer cells of the hormones they need to grow. The most common hormone therapy drugs are tamoxifen, and the aromatase inhibitors - Arimidex, Aromasin, and Femara.

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.

Recurrence of ILC

As noted, ILC is harder to diagnose than IDC; although with diagnosis tools improving all the time, the challenge is, thankfully, diminishing.

ILC is also more likely to occur in both breasts than IDC. But the difference isn't huge: there's a 15 percent chance IDC will happen in both breasts, while with ILC it's 20 percent. In the past, doctors might recommend a prophylactic (preventive) mastectomy of the unaffected breast for women with ILC; but this isn't a common recommendation anymore, particularly since treatment has become so much more effective.

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.