The first key difference is based on how far the cancer cells have spread.
In situ carcinoma
In situ carcinoma is a pre-cancerous lesion where abnormal cells stay inside the ducts or lobules of the breast, without invading the surrounding tissue. It represents around 20% of first breast cancer diagnoses. It cannot usually be felt and may be present at the same time in several milk ducts*.1,2
Although it is not yet an invasive cancer, it must be treated to prevent it from developing. The treatment of the disease is based on the surgical removal of the tumor and the surrounding tissue. Depending on the extent of the surgery, additional treatments such as radiotherapy, chemotherapy, or endocrine (hormone) therapy may be required*.
Infiltrating (or invasive) carcinoma
When cancer cells cross the barrier of the ducts or lobules to invade nearby tissues, this is called infiltrating carcinoma. These cells can then spread through the blood or lymphatic system to other regions of the body and form metastases.
Metastatic BREAST cancer
Metastatic BREAST cancer is not a separate histological type: it can develop from any of the subtypes described above. Metastases are cancer cells that move and grow in Other organs, creating a secondary lesion. The most common locations are the bones, liver, lungs, Brain and lymph nodes.
Current Treatment options include targeted therapies for HER2+ Profiles and new generations of antibody conjugates, which in most cases can control the disease effectively over the long term.
Depending on their origin: ductal or lobular
95% of breast cancers are adenocarcinomas that develop from the epithelial cells of the mammary gland. Among them, two types are different depending on where they start:3
Ductal carcinoma
Ductal carcinoma (also called IDC, Invasive Ductal Carcinoma) develops in the milk ducts. It is the most common type: it accounts for more than 80% of breast cancer diagnoses.4,5
Lobular carcinoma
Lobular carcinoma (ILC, Invasive Lobular Carcinoma) starts in the breast lobules. It accounts for around 15% of breast tumours. Its specific characteristics: it spreads in a diffuse way instead of forming a clear mass, which can sometimes make it harder to detect on a mammogram.6
There are also rarer forms, such as papillary or mucinous carcinomas, which have specific biological characteristics and a generally favorable outlook.
According to their biological Profile: three molecular subtypes
Beyond where they start in the body, breast cancers are different depending on the receptors on the surface of their cells. This biological Profile is important for choosing the right Treatment.
Hormone-dependent breast cancer (HR+)
Hormone-dependent breast cancer has receptors for estrogen and/or progesterone. Sex hormones stimulate the growth of these cancer cells. It is the most common subtype, accounting for about 70 to 80% of all breast cancers, and it has the best outlook among the three molecular subtypes.7
Treatment includes hormone therapy, usually prescribed for 5 years after Surgery. For Women who have not reached menopause, this is most often tamoxifen; for Women who have reached menopause, it is aromatase inhibitors.7
HER2-positive breast cancer (HER2+)
HER2-positive breast cancer is marked by too much HER2 protein on the surface of tumour cells, which stimulates their growth. It accounts for about 14% of breast cancers in Women.8
For a long time, it was linked to a less favorable outlook, but its development has changed with targeted anti-HER2 therapies. Trastuzumab, given after Surgery and chemotherapy, significantly improves survival without the disease, regardless of lymph node involvement.9
Triple-negative breast cancer (TNBC)
Triple-negative breast cancer does not have any of the three receptors identified as treatment Targets: estrogen, progesterone and HER2. It accounts for 10 to 15% of new breast cancers and has the least favorable outlook among the subtypes. It is more common in Black and premenopausal Women, and in patients with a BRCA1 mutation.10
When there is no hormone or HER2 target, chemotherapy is the main Treatment, often given Before surgery (neoadjuvant chemotherapy) to assess the tumour response. Immunotherapy is now a Major advance for certain TNBC Profiles.
Key points to remember
Every BREAST cancer is unique. Its histological type, biological Profile and stage at diagnosis Total shape the Treatment strategy. This is why the diagnostic assessment is so detailed: it is not only about finding a Tumour, but also about fully describing it to choose the most suitable Treatment for each patient.
Chiappa C, Bonetti A, Jaber GJ, De Berardinis V, Bianchi V, Rovera F. Pure Ductal Carcinoma In Situ of the Breast: Analysis of 270 Consecutive Patients Treated in a 9-Year Period. Cancers (Basel). 2021 Jan 23;13(3):431. doi: 10.3390/cancers13030431. PMID: 33498737; PMCID: PMC7865419.
Makki, J. (2015). Diversity of breast carcinoma: histological subtypes and clinical relevance. Clinical Medicine Insights Pathology, 8, 23–31.https://doi.org/10.4137/cpath.s31563
Batra H, Mouabbi JA, Ding Q, Sahin AA, Raso MG. Lobular Carcinoma of the Breast: A Comprehensive Review with Translational Insights. Cancers (Basel). 2023 Nov 20;15(22):5491. doi: 10.3390/cancers15225491. PMID: 38001750; PMCID: PMC10670219.
Walsh, E. M., Smith, K. L., & Stearns, V. (2020). Management of hormone receptor-positive, HER2-negative early breast cancer. Seminars in Oncology, 47(4), 187–200.https://doi.org/10.1053/j.seminoncol.2020.05.010
Tommasi C, Airò G, Pratticò F, Testi I, Corianò M, Pellegrino B, Denaro N, Demurtas L, Dessì M, Murgia S, Mura G, Wekking D, Scartozzi M, Musolino A, Solinas C. Hormone Receptor-Positive/HER2-Positive Breast Cancer: Hormone Therapy and Anti-HER2 Treatment: An Update on Treatment Strategies. J Clin Med. 2024 Mar 24;13(7):1873. doi: 10.3390/jcm13071873. PMID: 38610638; PMCID: PMC11012464.
Yao J, Zhang Y, Chen M, Yamashita T, Liu Y, Zheng S. Efficacy and safety analysis of a docetaxel-plus-trastuzumab regimen in patients with early-stage HER2-positive breast cancer: a retrospective single-arm study. Gland Surg. 2025 Feb 28;14(2):219-227. doi: 10.21037/gs-2024-549. Epub 2025 Feb 25. PMID: 40115851; PMCID: PMC11921364.
Zagami P, Carey LA. Triple negative breast cancer: Pitfalls and progress. NPJ Breast Cancer. 2022 Aug 20;8(1):95. doi: 10.1038/s41523-022-00468-0. PMID: 35987766; PMCID: PMC9392735.
Last updated on 28/10/2026
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