Types of Breast Cancer and the Latest Research

Breast cancer is the most commonly diagnosed cancer in Canadian women. According to the Canadian Cancer Society, approximately 1 in 8 women in Canada will develop breast cancer in their lifetime. Yet despite its prevalence, breast cancer is not a single, uniform disease. It encompasses a spectrum of subtypes each with distinct biological characteristics, treatment implications, and prognoses. 

Understanding the type of breast cancer you or someone you love has been diagnosed with is an important step in navigating treatment decisions, understanding research, and knowing what questions to ask your care team. Here is a comprehensive overview of the main types of breast cancer and the latest research that is changing outcomes.

How is Breast Cancer Classified?

Breast cancers are classified in two main ways: 

• By location: Where in the breast the cancer originated, whether in the milk ducts (ductal) or the milk-producing lobules (lobular). 
• By receptor status: Whether the cancer cells are driven by hormones (estrogen/progesterone receptors) or a protein called HER2, which determines which targeted therapies will be most effective.

What Are The Main Types of Breast Cancer? 

1. Invasive Ductal Carcinoma (IDC) 

Invasive ductal carcinoma is the most common type of breast cancer, accounting for approximately 70–80% of all diagnoses. IDC begins in the milk ducts of the breast and then grows into the surrounding breast tissue. The term “invasive” means it has broken through the duct wall but does not necessarily mean it has spread to other parts of the body. 

What would an IDC breast lump feel like? It typically presents as a firm, irregular mass that may feel fixed (not easily moved). However, IDC can also be detected on imaging before a lump is felt at all, which is why it’s so important to have routine mammograms. 

2. Invasive Lobular Carcinoma (ILC) 

ILC begins in the milk-producing lobules and accounts for about 10–15% of invasive breast cancers. It is distinct from IDC in that it tends to grow in a single-file pattern rather than forming a discrete mass, which makes it harder to detect on mammography and easier to miss on self-examination. An MRI is often more effective for evaluating ILC. 

3. Ductal Carcinoma In Situ (DCIS) 

DCIS is a non-invasive (Stage 0) breast cancer in which abnormal cells are confined within the milk ducts and have not yet spread to surrounding tissue. It is the most commonly diagnosed non-invasive breast cancer. While DCIS is not immediately life-threatening, it significantly raises the risk of developing invasive breast cancer and is typically treated to prevent progression. 

4. Triple-Negative Breast Cancer (TNBC) 

Triple-negative breast cancer is defined by the absence of all three receptor types: estrogen receptors (ER-), progesterone receptors (PR-), and HER2 (HER2-). This means it cannot be treated with hormone therapies or HER2-targeted drugs, which historically made it the most challenging subtype to treat. 

TNBC accounts for roughly 10–15% of all breast cancers and tends to grow and spread more aggressively. It disproportionately affects younger women and women of African descent. However, immunotherapy has dramatically changed outcomes for TNBC patients in recent years, representing one of the most significant research breakthroughs in breast cancer treatment. 

5. HER2-Positive Breast Cancer 

HER2-positive breast cancers produce excess quantities of the HER2 protein, which promotes cancer cell growth. They tend to grow faster than hormone receptor-positive cancers but respond well to targeted anti-HER2 therapies such as trastuzumab (Herceptin), pertuzumab, and the newer antibody-drug conjugate trastuzumab deruxtecan (T-DXd). HER2-positive cancers account for about 15–20% of all breast cancer diagnoses. 

6. Inflammatory Breast Cancer (IBC) 

Inflammatory breast cancer is a rare but aggressive form of breast cancer that accounts for 1–5% of diagnoses. Unlike most breast cancers, IBC rarely presents as a lump. Instead, it causes redness, swelling, warmth, and a dimpled texture (often described as an “orange-peel” skin appearance) that can look like an infection or rash. Because IBC can be mistaken for mastitis, it is often diagnosed at a later stage. Any breast that presents with these skin changes should be evaluated promptly. 

7. Hormone Receptor-Positive (HR+) Breast Cancer 

The most common breast cancer subtype overall, HR+ cancers are fuelled by estrogen (ER+), progesterone (PR+), or both. These cancers are typically slower-growing and highly responsive to hormonal therapies (such as tamoxifen and aromatase inhibitors) which block the hormones that feed them. HR+ cancers have excellent long-term outcomes with appropriate treatment, though they carry a risk of late recurrence that differs from other subtypes. 

The Latest Breast Cancer Research: What’s Changing Outcomes 

Breast cancer research is moving rapidly. Here are some of the most significant recent advances: 

Blood Test for Breast Cancer (Liquid Biopsy) 

One of the most exciting frontiers in breast cancer research is the blood test for breast cancer, also known as a liquid biopsy. These tests detect circulating tumour DNA (ctDNA) shed by cancer cells into the bloodstream. They show promise for early detection, monitoring treatment response, and detecting recurrence earlier than imaging. While not yet standard clinical practice, liquid biopsies are advancing quickly and may change how breast cancer is monitored in the coming years. 

Antibody-Drug Conjugates (ADCs) 

ADCs are a newer class of targeted therapies that deliver chemotherapy directly to cancer cells via a targeting antibody. Trastuzumab deruxtecan (Enhertu) has shown remarkable results in HER2-positive and even HER2-low breast cancers, significantly extending survival. This has broadened treatment eligibility beyond patients with high HER2 expression. 

Immunotherapy for Triple-Negative Breast Cancer 

The approval of pembrolizumab (Keytruda) combined with chemotherapy has been a landmark development for early-stage and metastatic TNBC. Immunotherapy, which harnesses the patient’s own immune system to fight cancer, has meaningfully improved outcomes for a subtype that previously had limited options. 

Precision Medicine and Genetic Testing 

Advances in genetic testing (BRCA1, BRCA2, PALB2, and others) are enabling more personalized treatment planning. PARP inhibitors (drugs that exploit weaknesses in DNA repair in BRCA-mutated cancers) have shown strong efficacy in both early and metastatic settings. For patients with a family history, genetic counselling is increasingly important. 

Mammogram Screening and AI 

Artificial intelligence is being integrated into mammography interpretation with promising results. Studies have shown that AI-assisted mammogram screening can detect cancers that human readers miss, reduce false positives, and improve overall screening accuracy. This technology is gradually being adopted in screening programs worldwide, including in Canada. 

For the most up-to-date information on Canadian breast cancer research, Cancer Research Canada is an excellent resource for tracking the latest studies and clinical trials.

Expert Breast Cancer Care at VM Med: Dr. Naim Otaky 

At VM Med’s Breast Centre in Montreal, our team provides expert, personalized breast cancer care from screening and diagnosis to surgery and oncology follow-up, all under one roof. 

Dr. Naim Otaky (M.D., F.R.C.S.(C)) is the Medical Director of VM Med and a Breast & Thyroid Specialist and General Surgeon. Dr. Otaky completed his medical training at McGill University in 1998 and his general surgery residency training at McGill in 2003, earning the designation of Fellow of the Royal College of Physicians and Surgeons of Canada. He has been published in several well-regarded academic journals, has lectured at international breast conferences, and in 2008 performed live surgery to an international audience of breast experts at The Breast Course. He is a staff surgeon at the McGill University Health Centre Lachine Campus and Jean-Talon Hospital. 

As the largest private breast centre in Canada, VM Med offers comprehensive breast health services, including breast imaging (mammography, ultrasound, MRI), breast biopsy, surgical consultation, breast cancer staging, oncology care, and genetic testing, all available in a single visit without the delays of the public system. 

To book a consultation with Dr. Otaky or a member of our breast team, call or fill out our online form. 

Additional Resources 

For more information, explore our VM Med blogs, including Breast Cancer: Early Detection & What Happens At Each Stage and Breast Cancer in Younger Women: What You Need to Know. 

Still have questions? Book a consultation with our experts. Our team of health experts takes care of every aspect of our patients’ breast health needs and works with you to create a personalized course of treatment.