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Invasive ductal carcinoma (IDC)

The information on this page was reviewed and approved by
Maurie Markman, MD, President, Medicine & Science at CTCA.

This page was updated on September 21, 2021.

Invasive ductal carcinoma (IDC) is the most common form of invasive or spreading breast cancer. IDC accounts for about 80 percent of invasive breast cancer cases, according to the American Cancer Society. It may also be called infiltrating ductal carcinoma. The cancer starts in the milk ducts, which are tasked with carrying milk from the breast to the nipples for breastfeeding.

Unlike ductal carcinoma in situ (DCIS), where the cancer cells are only found in the lining of the ducts, invasive ductal carcinoma means cancer cells have spread outside of the milk ducts to other parts of the breast. Depending on when it’s caught and how aggressive the tumor is, the breast cancer may spread to lymph nodes and throughout the body. The patient may feel the breast lump, as it tends to grow as a solid mass.

Below are four types of invasive ductal carcinoma that are less common:

Medullary ductal carcinoma: This type of cancer is rare and accounts for 3 percent to 5 percent of breast cancers. It is called “medullary” because, under a microscope, it resembles part of the brain called the medulla. Medullary carcinoma may occur at any age, but it typically affects women in their late 40s and early 50s. Medullary carcinoma is more common in women who have a BRCA1 gene mutation. Medullary tumors are often “triple-negative,” which means they test negative for estrogen and progesterone receptors and for the HER2 protein. Medullary tumors are less likely to involve the lymph nodes, are more responsive to treatment, and may have a better prognosis than more common types of invasive ductal cancer.

Mucinous ductal carcinoma: This type of breast cancer accounts for less than 2 percent of breast cancers. Microscopic evaluations reveal that these cancer cells are surrounded by mucus. Like other types of invasive ductal cancer, mucinous ductal carcinoma begins in the milk duct of the breast before spreading to the tissues around the duct. Sometimes called colloid carcinoma, this cancer tends to affect women who have gone through menopause. Mucinous cells are typically positive for estrogen and/or progesterone receptors and negative for the HER2 receptor.

Papillary ductal carcinoma: This cancer is also rare, accounting for less than 1 percent of invasive breast cancers. In most cases, these types of tumors are diagnosed in older, postmenopausal women. Under a microscope, these cells resemble tiny fingers or papules. Papillary breast cancers are typically small, and test positive for the estrogen and/or progesterone receptors and negative for the HER2 receptor. Most papillary carcinomas are invasive and are treated like invasive ductal carcinoma.

Tubular ductal carcinoma: Another rare type of IDC, this cancer makes up less than 2 percent of breast cancer diagnoses. Like other types of invasive ductal cancer, tubular breast cancer originates in the milk duct, then spreads to tissues around the duct. Tubular ductal carcinoma cells form tube-shaped structures. Tubular ductal carcinoma is more common in women older than 50. Tubular breast cancers typically test positive for the estrogen and/or progesterone receptors and negative for the HER2 receptor.

Invasive ductal carcinoma risk factors

Many factors may raise the risk of developing breast cancer. Some—such as genetics, gender and age—can't be changed. Others—such as alcohol use—are modifiable and within a person’s control.

There are a handful of genes known to increase the risk for breast cancer, most notably BRCA1 and BRCA2, the so-called breast cancer genes. Being female and getting older also increases the chances of developing breast cancer. Breast cancer is most often seen in women older than 50.

If a woman got her first menstrual period before age 12 or entered menopause after age 55, the risk is also elevated due to prolonged exposure to female sex hormones.

Reproductive history is another risk factor. The chances of developing breast cancer are higher for a woman whose first pregnancy was after age 30, who didn’t breastfeed or never had children. But remember, having risk factors doesn't always mean a person will have the disease.

Breast density matters, too, and increases breast cancer risk. Dense breasts also make it harder to visualize cancer on a mammography. Doctors may suggest additional testing for patients with dense breasts.

Other risks for breast cancer include:

  • Personal history of breast cancer
  • History of noncancerous breast disease such as usual hyperplasia, which is characterized by quickly growing cells that look normal under a microscope
  • History of radiation to the chest area
  • Use of diethylstilbestrol (DES) to stave off miscarriage. A patient whose mother took DES is at higher risk for breast cancer, too. This drug is no longer used in humans.

Many women will develop breast cancer without any of these risk factors.

Reducing your risk for invasive ductal carcinoma

Anyone wanting to lower their risk for developing breast cancer should consider:

  • Exercising regularly
  • Losing weight if they’re overweight or obese
  • Speaking with their doctor about breast cancer risk when deciding on birth control pills or hormone replacement therapy (These medications may be associated with an increased risk of breast cancer, and the benefits and risks should be weighed when making any decisions.)
  • Cutting back on alcohol (The more alcohol consumed, the higher the risk for developing breast cancer, including invasive ductal carcinoma.)

When discussing breast cancer risk with a doctor, patients may want to ask for a personalized prevention strategy that includes screening guidelines.

Invasive ductal carcinoma diagnosis and treatment

Some women may feel a lump in their breast and seek evaluation, while others may learn they have breast cancer during their mammogram screening or breast X-ray. Other imaging tests and a biopsy may also be ordered to help the doctor assess the patient’s condition.

During a biopsy, the doctor removes some tissue or fluid from the breast for analysis under a microscope. The sample is sent off to a lab, where a pathologist checks for the presence of cancer cells, and it may take a few days to get the results.

If the diagnosis is breast cancer, the doctor then needs to determine its stage, including whether or not it’s started to spread inside or outside the breast. The specifics guide any treatment decisions.

The cancer is typically removed via surgery. This may be with a lumpectomy (where only the tumor is removed) or a mastectomy (removal of the entire breast). Breast reconstruction with implants or the patient’s own tissue may be considered after a mastectomy.

The surgeon may also remove lymph nodes to see whether the cancer is on the move.

The patient may also need other treatments if the cancer has started to spread. This includes chemotherapy or radiation to kill any errant cancer cells. Other options are hormonal therapy if the cancer tests positive for certain hormone receptors and/or targeted therapy if it expresses certain genetic markers. The cancer cells are analyzed to see whether they meet any of that criteria before treatment starts.

Sometimes it’s recommended that a patient start treatment with chemotherapy or hormonal therapy to shrink the tumor, so that it may be more easily removed with surgery.

Invasive ductal carcinoma survival rate

A five-year survival rate refers to the percentage of cancer patients who are alive five years after they were diagnosed. Keep in mind that these are estimates and based on past data, and advances in treatments may have improved these numbers.

If cancer has spread only within the breast, the five-year survival rate estimate is 99 percent, according to the American Society of Clinical Oncology (ASCO), and a majority of women with breast cancer (63 percent) receive a diagnosis at this stage.

If cancer has spread to the neighboring lymph nodes, the five-year survival rate is 86 percent, according to the ASCO, and if it’s spread to a distant part of the body (metastasis), the rate is 28 percent.

Tremendous strides in treating breast cancer, as well as diagnosing it earlier when it’s in more treatable stages, are helping to improve these statistics.

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