Invasive ductal carcinoma (IDC) — also called infiltrating ductal carcinoma — is the most common type of breast cancer. About 70 percent to 80 percent of breast cancers are IDC. Within the United States, approximately 180,000 people are diagnosed with IDC per year. Invasive ductal carcinoma is also the most common breast cancer seen in men.

What Is Invasive Ductal Carcinoma?

Doctors divide breast cancers into types depending on where the cancer starts and how far it spreads. IDC begins in cells that make up the milk ducts, which carry milk from the breast lobules, where it is made, to the nipple. Ductal carcinoma in situ (DCIS) is another type of breast cancer that develops in cells of the milk ducts. In DCIS, the cancer stays inside the milk ducts.

A growing tumor can eventually spread. Breast cancer is called “invasive” when it grows into the surrounding tissue. IDC develops when milk duct cells turn cancerous and then spread into the nearby fatty or connective tissue within the breast. Eventually, IDC may also metastasize (spread to more distant parts of the body). Other types of invasive breast cancer include invasive lobular carcinoma, triple-negative breast cancer, and inflammatory breast cancer.

What Causes IDC?

Breast cancer develops when cells in the breast undergo gene changes that cause them to grow abnormally. Sometimes, these gene changes are inherited — they are passed down within families and are present at birth. Often, these inherited mutations occur in the genes BRCA1 or BRCA2.

For 9 out of 10 people with breast cancer, gene changes occur randomly over the course of a person’s life. Certain risk factors increase the chances that a person develops IDC. These may include:

• Being a woman
• Being over the age of 55
• Having had breast cancer or other breast conditions in the past
• Having family members who have had breast cancer
• Receiving radiation therapy in the area of the chest
• Using hormone replacement therapy
• Being obese
• Getting low levels of physical activity
• Smoking tobacco
• Drinking a lot of alcohol
• Having dense breast tissue (naturally having higher levels of connective tissue and lower levels of fat tissue in the breasts)
• Being a member of a particular ethnic group (e.g., Ashkenazi Jewish, Norwegian, Dutch, Icelandic), according to the National Cancer Institute

Some people have many of these risk factors and never develop IDC, whereas others have no risk factors and are diagnosed with cancer. Doctors don’t usually know why a particular person does or does not develop breast cancer.

Symptoms of IDC

IDC symptoms are similar to those seen in other types of breast cancer. These may include:

• A lump in the breast or armpit
• Swelling in the breast
• Skin changes on one breast, including discoloration, thickening, irritation, a rash, or dimpling
• An inverted nipple
• Discharge coming from the nipple
• Breast or nipple pain

Some people don’t experience any signs or symptoms of breast cancer. Instead, they only find out that something is wrong when they undergo a mammogram (an imaging test that helps screen for breast cancer).

Other health conditions besides breast cancer can cause breast changes, and experiencing any of these symptoms does not necessarily mean that you have cancer. However, you should always report any changes in breast appearance to your doctor.

Invasive Ductal Carcinoma Diagnosis

Your doctor may recommend additional tests if you notice symptoms of breast cancer or if there are abnormalities on a screening mammogram. One possible test is a diagnostic mammogram, which takes more detailed images of the breast than a screening mammogram. Other imaging tests, such as an ultrasound or magnetic resonance imaging (MRI), can also help identify any potential problems within the breast.

A biopsy is the only test that can officially diagnose breast cancer. During a biopsy, a doctor uses a needle to remove one or more samples of tissue from the breast. In rare cases, doctors may recommend surgery to remove a larger biopsy sample.

Biopsy tissue samples are sent to a laboratory for further testing. There, tests can show whether cells in the sample are cancerous. If cancer is found, tests can identify the type of cancer, the grade (how fast cancer cells are growing), and the cancer’s molecular subtype.

The molecular subtype describes which proteins are found on the surface of cancer cells. This includes whether a cell makes too much of a protein called human epidermal growth factor receptor 2 (HER2). The molecular subtype also includes, among other markers, whether the cell surface contains proteins called hormone receptors — either estrogen receptor (ER) or progesterone receptor (PR). Breast cancers that are HER2-positive or hormone receptor-positive may be treatable with targeted therapy or hormone therapy drugs.

Staging IDC

If you are diagnosed with IDC, your doctor will perform additional tests to determine the cancer stage. The stage tells you how large the cancer is and how far it has spread. Stages range from 1 to 4, and stage numbers are sometimes written in Roman numerals, such as stage IV instead of stage 4.

The higher a breast cancer’s stage, the more advanced it is. The recently revised stages of IDC are:

• Stage 1 — The tumor is very small and found in just one part of the breast.
• Stage 2 — The tumor is slightly larger, or breast cancer cells have spread to nearby lymph nodes.
• Stage 3 — The tumor has spread throughout the breast, nearby lymph nodes, and surrounding tissue.
• Stage 4 — The cancer is metastatic and is found in other places of the body, such as the liver, bones, brain, or distant lymph nodes.

Cancer may also be described as:

• Localized — The cancer is limited to the place where it started, with no sign that it has spread.
• Regional — The cancer has spread to nearby lymph nodes, tissues, or organs.
• Distant — The cancer has spread to distant parts of the body.

In order to figure out whether cancer has metastasized, your doctor may run blood tests. These may identify that breast cancer is present in another organ. A doctor will perform a physical exam and may run additional imaging tests such as a bone scan, computed tomography (CT), or positron emission tomography (PET)/CT scan. These scans allow doctors to see cancer cells in other parts of the body.

Treatment of IDC

People with breast cancer are often treated with surgery, radiation therapy, chemotherapy, targeted therapy, or hormone therapy. The exact breast cancer treatment plan that you receive depends on your cancer stage, grade, HER2 status, and hormone-receptor status, as well as your age, general health, and personal preferences.

Surgery

Most people with IDC undergo surgery to remove the tumor and possibly the nearby lymph nodes. Possible surgical treatment options may include:

• Lumpectomy or breast-conserving surgery (BCS) — The surgeon takes out the tumor and a small amount of surrounding healthy breast tissue.
• Mastectomy — The surgeon removes all of the breast tissue.
• Sentinel lymph node biopsy — The surgeon removes one, two, or three nearby lymph nodes, mostly for informational purposes.
• Axillary lymph node dissection — The surgeon takes out many lymph nodes (in cases where cancer cells have likely started spreading to the lymphatic system).

Most people with localized IDC will undergo surgery as their first treatment. People with regional cancer may receive chemotherapy first, in order to shrink the tumor before surgery. For those who are diagnosed with distant IDC, surgery is unlikely to remove all of the cancer. However, different types of surgeries may be used to reduce symptoms or to remove tumors in certain parts of the body.

Radiation Therapy

During radiation therapy, high-energy particles or beams are directed at a particular part of the body. People with IDC may receive radiation treatments to the breast, underarm, collarbone, or chest, or to areas of distant spread that are causing pain or problems.

Most people who choose to get BCS need radiation treatments after surgery is done. This helps get rid of any cancer cells that may remain in the breast.

Chemotherapy

Chemotherapy drugs damage and kill cancer cells. These medications can reach all parts of the body, so they can help treat cancer that has begun to spread.

Not everyone with IDC receives chemotherapy. Doctors may recommend chemotherapy for people with advanced (higher-stage) cancer or larger tumors. Chemotherapy drugs may be given before surgery, to shrink a tumor before it is removed. They may also be a good option after surgery, to help kill any remaining cancer cells and prevent the cancer from returning.

There are many chemotherapy drugs that doctors may recommend for people with IDC. Some of these include:

• Adriamycin (doxorubicin)
• Adrucil (fluorouracil or 5-FU)
• Cytoxan (cyclophosphamide)
• Ellence (epirubicin hydrochloride)
• Taxol (paclitaxel)
• Taxotere (docetaxel)

Targeted Therapy

Targeted therapy drugs recognize and attach to specific genes or proteins found within cancer cells. This helps keep cancer cells from growing and kills the cells.

Several targeted therapies can help treat HER2-positive IDC. Cancer cells that contain high levels of HER2 rely on this protein to grow, so drugs that block HER2 can kill these cells. These targeted therapy drugs include:

• Herceptin (trastuzumab)
• Kadcyla (ado-trastuzumab emtansine)
• Nerlynx (neratinib)
• Perjeta (pertuzumab)
• Phesgo (a combination of pertuzumab, trastuzumab, and hyaluronidase-zzxf)

Other targeted therapy drugs recognize and block other proteins found in cancer cells. Options may include:

• Cyclin-dependent kinase (CDK) 4 and CDK6 inhibitors — These may help treat hormone receptor-positive cancers.
• Mammalian target of rapamycin (mTOR) inhibitors — These may be an option for those with hormone receptor-positive, HER2-negative IDC who have already gone through menopause.
• Phosphoinositide 3-kinases (PI3K) inhibitors — These may treat cancer cells that contain a mutation in the PIK3CA gene.
• Poly (ADP-ribose) polymerase (PARP) inhibitors — These can help treat people with mutations in the BRCA genes.

Hormone Therapy

Cancer cells that contain the hormone receptors ER and PR rely on hormones in order to grow. People with hormone receptor-positive IDC usually receive hormone therapy to block the effects of the hormones naturally produced by the body.

One common hormonal therapy is tamoxifen. This drug attaches to a cancer cell’s hormone receptors and prevents the body’s hormones from reaching the cell. Another type of hormone therapies, aromatase inhibitors, are most often used by women who have gone through menopause. These drugs cause the body to make lower amounts of estrogen.

Clinical Trials

People with IDC may want to consider taking part in a clinical trial — a study in which cancer researchers test new treatments. Clinical trials allow people with breast cancer to access new treatment options that may not otherwise be available. Talk to your health care team if you are interested in participating in a clinical trial.

What Is the Outlook for IDC?

IDC prognosis largely depends on how far the cancer has spread. Among those with invasive breast cancer that has not metastasized, about 9 out of 10 people will live for five years or more after being diagnosed. Additionally, 84 percent will live at least 10 years.

If invasive breast cancer has spread to nearby lymph nodes, the survival rates are slightly lower. About 86 percent of people will live for five years or more. Additionally, about 28 percent of people with metastatic breast cancer will live at least five years.

Other factors besides stage also affect a person’s breast cancer outlook. Younger women and Black women tend to have worse outcomes when they are diagnosed with breast cancer, according to Cancer.Net. A person’s overall health, as well as their cancer’s grade and molecular subtype, also affect prognosis. If you would like to learn more about your individual outlook, talk to your doctor, who is familiar with your cancer’s specific characteristics.

Talk With Others Who Understand

MyBCTeam is the social network for people with breast cancer and their loved ones. On MyBCTeam, more than 53,000 members come together to ask questions, give advice, and share their stories with others who understand life with breast cancer.

Are you living with invasive ductal carcinoma? Share your experiences in the comments below, or start a conversation by posting on MyBCTeam.