Types of Breast Cancer

The type, subtype, and stage of your breast cancer help doctors understand its characteristics and determine what treatments are likely to work best. Each type behaves differently and may respond to different treatments. Your healthcare team will use imaging, pathology reports, and biomarker tests to assess the specific features of your cancer and develop a personalized treatment plan.

Breast cancers are classified as:

• Non-Invasive (In Situ): Cancer cells stay inside the milk ducts or lobules and have not spread
• Invasive: Cancer cells have spread into the surrounding breast tissue

Most breast cancers are adenocarcinomas, meaning they develop in glandular tissue. This includes:

• Ductal Carcinomas: Begins in the milk ducts
• Lobular Carcinomas: Begins in the milk-producing glands (lobules)

Non-Invasive Breast Cancers

Ductal Carcinoma in Situ (DCIS)
DCIS is an early-stage, non-invasive cancer where abnormal cells are found within the milk ducts but have not spread to surrounding breast tissue. It is classified as Stage 0 and is often detected through screening mammograms. While DCIS has a high survival rate, it may develop into invasive cancer over time, requiring careful monitoring and treatment.

Lobular Carcinoma in Situ (LCIS)
LCIS involves abnormal cells within the lobules of the breast. Despite the term “carcinoma,” LCIS is not considered breast cancer, but it is linked to an increased risk of developing invasive breast cancer in the future. LCIS is typically diagnosed through a biopsy rather than imaging. For more information on LCIS, visit our section on High-Risk Conditions.

Invasive Breast Cancers

Invasive Ductal Carcinoma (IDC)
IDC is the most common type of invasive breast cancer, accounting for 80% of cases. It begins in the milk ducts and spreads into surrounding breast tissue.

Some IDCs have unique features that affect their behavior and response to treatment, including:

• Secretory Breast Carcinoma – A rare, slow-growing form with mucin-secreting cells. Despite a generally better prognosis, it can metastasize and recur, requiring aggressive treatment with surgery, radiation, and chemotherapy. It accounts for less than 0.15% of all infiltrating breast carcinomas.
• Metaplastic Breast Cancer – A rare, fast-growing form where cancer cells change into different types, such as squamous or mesenchymal-like cells. It is harder to treat and often requires surgery, radiation, and chemotherapy. Metaplastic breast cancer accounts for less than 1% of all breast cancers.
• Medullary, Mucinous, Papillary, and Tubular Carcinomas – Less common forms that generally have a better prognosis than standard IDC. This is often due to lower lymph node involvement, and, in some cases, better responses to treatment.

Invasive Lobular Carcinoma (ILC)
ILC begins in the lobules (milk-producing glands) and spreads to nearby breast tissue. Unlike IDC, ILC can be more challenging to detect on mammograms and often requires additional imaging. It accounts for about 10% of invasive breast cancers and may be found in both breasts.

For more information, visit the Lobular Breast Cancer Alliance or join Living with Lobular Breast Cancer in Canada, a private Facebook group that shares research and resources for those with ILC.

Other Types of Breast Cancer
Some types of breast cancer have distinct characteristics that affect their behavior, aggressiveness, and treatment options.

Inflammatory Breast Cancer (IBC)
IBC is a rare and aggressive form of breast cancer, accounting for 1-5% of all cases. Unlike most breast cancers, it typically develops without a distinct lump. Instead, cancer cells block lymph vessels in the skin, causing symptoms to appear quickly such as redness, swelling, warmth, and skin dimpling (peau d’orange). These changes can look like an infection (like mastitis) but do not respond to antibiotics. More common in younger individuals and people of African descent, IBC progresses quickly. Because it may not appear on mammograms, a biopsy is essential for diagnosis.

Paget’s Disease of the Breast
Paget’s disease of the breast is a rare form of breast cancer affecting the nipple and often the areola. It typically presents with itching, redness, flaking, and crusting, which can be mistaken for eczema or other benign skin conditions. Unlike typical skin conditions, these symptoms don’t go away and do not improve with standard treatments. Paget’s disease is usually linked to underlying DCIS or invasive breast cancer. Because early signs can be misleading, diagnosis is often delayed. Prognosis varies depending on whether invasive cancer is present and if it has spread to nearby lymph nodes. A biopsy is required for diagnosis.

Medical Review by Roochi Arora, MD, FRCPC, August 2025

Our Stories

More Stories

Tell Us your Story