Invasive ductal breast cancer (IDC) is a cancer that has originated in the cells that line the ducts of the breast but has begun to spread to surrounding breast tissue, with the potential to spread to other parts of the body. IDC is the most common type of breast cancer, accounting for 75% of all cases diagnosed. IDC is also the type of breast cancer that most commonly affects men.

If an individual has been diagnosed with ductal carcinoma in situ (DCIS), the cancer is contained within the milk duct, has not invaded other areas and does not class as IDC.

Symptoms

The potential symptoms of IDC that should be checked for in a breast self-exam include:

• A change in the size or shape of a breast
• A lump in the breast or underarm area
• A thickening of the breast skin
• Changes in appearance of the nipple or breast that differ from usual changes
• Nipple discharge
• Rash or redness of the breast
• Dimpling around the nipple or on the breast skin
• Pain or swelling in the breast, nipple or armpit

Screening

Cancer in the breast can be detected on routine screening before symptoms arise and some women get diagnosed with IDC after attending breast screening even in the absence of any symptoms such as those described above.

Breast screening usually involves a physical breast examination and one or more of the following: mammogram (breast x-ray), ultrasound of the breast and under-arm area, fine needle aspiration and/or a biopsy.

Examining breast cancer cells under the microscope

When a breast cancer biopsy is examined under a microscope, there are two things a pathologist is looking for:

Cells with a unique appearance

Subtypes of invasive ductal carcinoma that describe the cells’ appearance include tubular, mucinous, medullary and papillary. Identifying the subtype provides clues about prognosis and how cells may respond to treatment.

Degree of difference between cancer cells and normal cells

The degree of difference between cancer cells and normal cells is described as the cancer's grade, which is based on a scale of 1 to 3, with grade 3 cancers being the most different and considered the most virulent.

Treatment

To decide on the most appropriate treatment, doctors generally take into account the cancer’s stage, grade and receptor status.

Surgery, however, is usually the first treatment approach used for IDC. This may be breast-conserving surgery, where the cancer is removed along with some of the bordering normal breast tissue, or a full mastectomy, where all breast tissue including the nipple area is removed.
Patients are usually offered a breast reconstruction which can be performed either during surgery or at a later date. Some women choose instead to opt for a breast prosthesis, which can be fitted inside the bra to replace all or part of the removed breast.

Physicians will also check whether cancer cells have spread from the breast to the lymph nodes under the arm and may take a lymph node sample or remove all of the nodes (a lymph node clearance).

Adjuvant or additional therapy such as chemotherapy, radiotherapy, hormone therapy and targeted therapies may be given to a patient after surgery, to reduce the risk of breast cancer cells returning in the same breast, spreading elsewhere in the body, or a completely new primary breast cancer developing in either breast.

• Chemotherapy, known of as neo-adjuvant chemotherapy, may be given before surgery.
• Patients who undergo breast-conserving surgery will usually be given radiotherapy to reduce the risk of the cancer manifesting again in the breast. Those who have a mastectomy may also be given radiotherapy but this is more likely if there is a high risk that cancer cells may have been left behind or when cancer cells are found in the lymph nodes.
• The growth of some breast cancers is dependent on circulating hormones such as oestrogen and progesterone. Breast cancer cells may have receptors that such hormones bind to and stimulate the cancer’s growth. Knowing whether or not breast cancer cells have these hormone receptors aids the choice of treatment.
• Cancers may therefore be defined as oestrogen receptor (ER) positive, progesterone receptor (PR) positive or hormone receptor (HR) negative. Hormone-blocking medications such as tamoxifen, can therefore be used to reduce the growth of ER and PR positive cancers, whereas for HR negative cancers hormone-based therapy is of no use.
• Targeted therapies such as trastuzumab (Herceptin) may be offered to individuals who are HER2- positive, which can be ascertained through breast tissue testing during biopsy or surgery.