Invasive Ductal Carcinoma

Invasive ductal carcinoma (IDC), also known as infiltrating ductal carcinoma, refers to the uncontrolled growth of cancerous cells, originating from the ducts of the breast tissue. The cancer cells may penetrate through the ductal wall, invading the stroma (i.e., the surrounding adipose and fibrous connective tissue of the breast). It is the most common form of invasive breast cancer, representing 50-70% of breast cancer diagnoses. 

The breast is composed of mammary glands surrounded by the stroma. The mammary glands are made up of 12 to 20 lobes, each of them containing many smaller lobules and even smaller alveoli. These alveoli, lobules, and lobes are connected through a network of milk ducts that drain the milk produced during lactation to the areola, or nipple. The development of IDC originates in these milk ducts. 

The most common cause of invasive ductal carcinoma is DNA damage and genetic mutations of the breast tissue cells. Damage to DNA can cause changes in various genes, like BRCA1 and BRCA2, that usually control cell growth, prolong cell survival, manage cell division, and prevent unwanted cell death. If such changes occur, they can progressively result in uncontrolled cell growth and become cancerous and potentially penetrate into the stroma. 

A wide variety of genetic and environmental risk factors can lead to DNA damage and the consequent development of invasive ductal carcinoma. An individual’s sex assigned at birth is a very important risk factor, as most breast cancers occur in those who have been assigned female at birth. Additionally, advanced age increases the possibility of any malignancy, including IDC, to form. Having a personal and/or family history of breast or ovarian cancer increases the likelihood of developing IDC. In addition, a history of invasive ductal carcinoma in one breast poses a greater risk for developing a second cancerous lesion in the other breast. 

Finally, increased exposure to hormones such as estrogen also increases the risk for developing malignancies originating from the breasts, such as IDC. Factors which increase estrogen include having menarche (i.e., the first menstrual period) before 12 years of age, having the first childbirth after 30 years of age, never experiencing pregnancy, and experiencing menopause (i.e., termination of the menstrual period) after the age of 55. Similarly, exposure to administered estrogen and progesterone, for instance through various contraceptive methods (e.g., the birth control pill and intrauterine device) or through hormone replacement therapy (e.g. for postmenopausal women) poses an additional risk.

To diagnose an invasive ductal carcinoma, a detailed medical history and physical examination, specifically of the breast and the underarm area, is necessary. Masses larger than 2 cm can usually be detected clinically. However, physical examination of the breast with no significant findings does not eliminate the possibility of an underlying invasive carcinoma. Therefore, further imaging may be required in order to reveal an IDC, which tends to grow as a dense, solid mass with calcifications.

Diagnosis most commonly occurs during annual screening mammography as most individuals present with few other symptoms. Digital mammography usually detects masses of 1 cm or larger. However, mammography is not sensitive for invasive ductal carcinoma in young women, whose breasts tend to be more dense; in these cases breast ultrasonography can be used. Ultrasonography is useful in assessing the consistency and size of breast lumps. Finally, magnetic resonance imaging (MRI) is ideal for describing lesions in soft tissues such as those found in the breast. Therefore, it is very reliable in the assessment of high-risk cases, such as when evaluating the response of neoadjuvant chemotherapy (i.e., use of chemotherapy to reduce the size of the tumor before surgery), or when planning breast conservation surgery.

A tissue biopsy is necessary to confirm the diagnosis of IDC. The biopsy may be performed through a fine-needle aspiration (FNA), core biopsy, or excisional biopsy.

Treatment options for invasive ductal carcinoma usually depend on the severity of each case. The basic principles of treatment are to minimize the chances of local recurrence as well as to reduce the risk of metastasis. Therefore, surgical removal of the primary lesion is the initial step towards treatment. Individuals may remove only the malignant lesion (i.e., lumpectomy), totally remove the affected breast (i.e., mastectomy) or even remove both breasts (i.e., bilateral mastectomy). Clinicians will also assess if cancerous cells have spread to other parts of the body via the lymph nodes.  If there is lymph node involvement, all the infiltrated lymph nodes are typically removed. 

In some cases, surgical treatment may be combined with radiation therapy to achieve better local control of the cancer. In more severe cases, when the cancer has spread to other parts of the body, systemic treatment options are preferred. Chemotherapy, hormonal therapies, targeted therapies (e.g., monoclonal antibodies, immunosuppressants), or a combination of these may be administered. In very advanced cases, where surgery offers small or even no improvement, palliative therapy may be offered.