Types of Breast Cancer: IDC, ILC, DCIS, Triple-Negative, HER2+, and More

Key Takeaways

• Breast cancer is not one disease — it is classified by where it starts (ductal vs. lobular) and by receptor profile (ER, PR, and HER2 status), and both classifications directly determine which treatments will work.

• Invasive ductal carcinoma (IDC) is the most common type, accounting for roughly 70–80% of all breast cancers; invasive lobular carcinoma (ILC) is the second most common at 10–15%.

• Ductal carcinoma in situ (DCIS) is a non-invasive, Stage 0 finding with an excellent prognosis; emerging clinical trials are exploring active surveillance as an alternative to surgery for low-grade DCIS.

• Triple-negative breast cancer (TNBC) lacks hormonal and HER2 drivers, making it historically harder to treat — but advances including immunotherapy (pembrolizumab), PARP inhibitors, and antibody-drug conjugates have meaningfully expanded treatment options.

• HER2-positive breast cancer was once among the most feared subtypes; targeted therapies such as trastuzumab (Herceptin), pertuzumab, and trastuzumab deruxtecan (T-DXd/Enhertu) have transformed outcomes. A newly recognized category — HER2-low — has also become targetable with T-DXd, following FDA approval in January 2025.

How Breast Cancer Is Classified

Breast cancer is classified in two ways — by the anatomical site of origin (where in the breast it begins) and by its molecular/receptor profile (ER, PR, and HER2 status). Understanding your specific type is critical because it directly determines which treatments are effective.

The anatomical classification tells oncologists whether cancer arose in the milk ducts (ductal) or the milk-producing lobules (lobular), and whether it has broken out of that structure into surrounding tissue (invasive) or remains confined (non-invasive). The molecular classification — based on whether cancer cells carry receptors for estrogen, progesterone, or the HER2 protein — tells the treatment team which targeted agents will work. A patient with the same stage and grade of breast cancer can receive radically different therapy depending on their receptor status.

Together, these two frameworks define four major intrinsic molecular subtypes that oncologists use for treatment planning:

• Luminal A — ER-positive and/or PR-positive, HER2-negative, low Ki-67 (slow-growing). Best overall prognosis.

• Luminal B — ER-positive, higher Ki-67, may be HER2-positive. More aggressive than Luminal A.

• HER2-enriched — ER-negative, PR-negative, HER2-positive. Historically aggressive, now highly treatable.

• Triple-negative/basal-like — ER-negative, PR-negative, HER2-negative. No targeted hormonal or HER2 drivers.

Knowing where your cancer sits within both the anatomical and molecular frameworks shapes every decision that follows — surgery type, systemic therapy, radiation, and eligibility for clinical trials.

Ductal vs. Lobular: Where Breast Cancer Begins

To understand breast cancer types, it helps to know a little about breast anatomy. The breast contains hundreds of small glands called lobules that produce milk. Milk travels through a network of thin tubes called ducts toward the nipple. Both structures — the lobules and the ducts — are lined with epithelial cells, and it is in these cells that most breast cancers originate.

Ductal cancers arise in the lining of the milk ducts and are by far the most common origin point, accounting for roughly 80% or more of all breast cancers. Lobular cancers arise in the lobule cells and account for approximately 10–15% of breast cancers. A smaller number of cancers arise from other cell types in the breast (connective tissue, nipple skin, stroma) and are classified separately.

Whether a cancer is ductal or lobular matters beyond simple taxonomy: lobular cancers, for example, tend to grow in a diffuse, single-file pattern that makes them harder to detect on imaging and more likely to involve multiple sites within the breast.

Invasive Ductal Carcinoma (IDC): The Most Common Type

What Is IDC?

Invasive ductal carcinoma is the most frequently diagnosed form of breast cancer, representing approximately 70–80% of all invasive breast cancers, according to the American Cancer Society. The term “invasive” means the cancer cells have broken through the wall of the milk duct and grown into the surrounding breast tissue. From there, cancer cells can potentially travel through the lymphatic system or bloodstream to reach other parts of the body, which is why staging and early detection matter so much.

IDC is often listed as “not otherwise specified” (NOS) on pathology reports. This means the cancer has the characteristics of ductal carcinoma but does not fit into a more specific subtype (such as tubular or mucinous carcinoma, described later). Think of IDC-NOS as a broad default category that encompasses the majority of duct-derived breast cancers.

Importantly, IDC itself is not a single molecular disease. An IDC tumor can be ER-positive, HER2-positive, triple-negative, or any receptor combination and it is that receptor profile, not just the IDC label, that drives treatment decisions.

Symptoms and Diagnosis of IDC

IDC often presents as a firm, irregularly shaped lump that feels different from the surrounding breast tissue. On mammography, IDC typically appears as a mass, sometimes with associated calcifications (small calcium deposits). However, not all IDC is palpable — many cases are detected on routine screening mammogram before any lump can be felt, which is one of the strongest arguments for adhering to recommended screening schedules.

A biopsy is always required to confirm the diagnosis. The biopsy sample is then analyzed for receptor status (ER, PR, HER2) and grade — information that is just as important as the IDC diagnosis itself for planning treatment.

Treatment for IDC

Treatment for IDC depends primarily on two factors: stage (how far the cancer has spread) and receptor profile (which molecular drivers are present). Most patients with early-stage IDC will have surgery — either a lumpectomy (breast-conserving) followed by radiation, or a mastectomy. Systemic therapy is then tailored to receptor status:

• ER-positive IDC: Hormone therapy (tamoxifen or aromatase inhibitors) forms the backbone of treatment. For intermediate-risk cases, the Oncotype DX genomic test helps determine whether chemotherapy adds meaningful benefit. CDK4/6 inhibitors (abemaciclib, ribociclib) are used in higher-risk early-stage and metastatic settings.

• HER2-positive IDC: HER2-targeted therapy (trastuzumab, pertuzumab) is added to chemotherapy; T-DM1 or T-DXd may be used in later-line settings.

• Triple-negative IDC: Chemotherapy is the foundation; pembrolizumab (immunotherapy) and sacituzumab govitecan are options depending on stage and biomarker status.

For early-stage, hormone receptor-positive IDC, the outlook is generally favorable. Five-year survival rates exceed 90% for Stage I and II disease.

Invasive Lobular Carcinoma (ILC): The Second Most Common Type

What Is ILC?

Invasive lobular carcinoma arises in the milk-producing lobules and accounts for approximately 10–15% of invasive breast cancers, making it the second most common type. Unlike IDC, which tends to form a distinct mass, ILC cells grow in a characteristic single-file pattern — infiltrating the surrounding breast tissue individually rather than clustering together into a palpable lump.

This growth pattern has important clinical consequences. ILC is much harder to detect by touch and can be difficult to see on standard mammography. It is also more likely to be multifocal (multiple tumor sites within the same breast) or bilateral (affecting both breasts).

From a molecular standpoint, ILC is overwhelmingly hormone receptor-positive, meaning the vast majority of ILC tumors are ER-positive and/or PR-positive. HER2 overexpression is relatively rare in ILC. This means most patients with ILC are candidates for hormone therapy, but the cancer’s unique growth pattern and tendency for multifocality still set it apart from ER-positive IDC in terms of surgical and treatment planning.

Challenges With ILC Diagnosis

Because ILC does not form a discrete mass, it frequently presents as a vague thickening or firmness in the breast rather than a classic lump. Standard digital mammography has lower sensitivity for ILC than for IDC, and the cancer is sometimes discovered at a more advanced stage than it would be if it formed a palpable mass. MRI of the breast is more sensitive than mammography for detecting ILC and is increasingly used in surgical planning and in women with a personal history of ILC.

If you receive an ILC diagnosis, your care team may recommend additional imaging — including contralateral breast MRI — to fully characterize the extent of disease before making surgical decisions.

Treatment for ILC

The overall treatment framework for ILC mirrors that of hormone receptor-positive IDC, with some important differences driven by its biology and growth pattern. Mastectomy is required more frequently than in IDC, particularly when disease is multifocal or when clear surgical margins cannot be achieved with lumpectomy. Hormone therapy (tamoxifen or aromatase inhibitors) is the central systemic treatment for the ER-positive tumors that constitute the large majority of ILC cases.

CDK4/6 inhibitors (abemaciclib, ribociclib, palbociclib) are increasingly used in higher-risk early-stage and metastatic ILC, consistent with their role across hormone receptor-positive breast cancer broadly. One nuance worth knowing: ILC generally responds less robustly to neoadjuvant (pre-surgery) chemotherapy than IDC, which is one reason hormone therapy-based neoadjuvant approaches are sometimes preferred for ILC.

Ductal Carcinoma In Situ (DCIS): Non-Invasive Breast Cancer

What Is DCIS?

Ductal carcinoma in situ is a non-invasive, Stage 0 finding in which abnormal cells are present inside the milk ducts but have not broken through the duct wall into surrounding breast tissue. It is sometimes called pre-invasive or pre-cancer, though the terminology is actively debated among researchers and clinicians. According to the American Cancer Society, DCIS accounts for approximately 20% of breast cancers detected through screening mammography.

The word “in situ” means “in place” — the cells have not yet invaded. A subset of DCIS, if left untreated, would progress to invasive breast cancer over time; however, not all DCIS carries the same risk of progression, and predicting which cases will progress remains an area of active research. DCIS is graded as low, intermediate, or high based on how abnormal the cells appear under the microscope, and grade correlates with progression risk.

Should DCIS Always Be Treated?

This is one of the most actively debated questions in breast oncology. The current standard of care for most DCIS involves surgery — either lumpectomy plus radiation (breast-conserving) or mastectomy — followed by hormone therapy for ER-positive DCIS. This approach is highly effective: DCIS treated according to current guidelines carries an excellent prognosis, and most patients are cured.

However, concern about overtreatment, particularly for low-grade DCIS that may never progress, has driven a wave of clinical trials testing active surveillance (monitoring without immediate surgery). The COMET trial, the largest US active surveillance trial for low-grade DCIS, presented results at the San Antonio Breast Cancer Symposium in late 2024, subsequently published in JAMA. At two years, the rate of ipsilateral invasive cancer was 4.2% in the active monitoring group versus 5.9% in the guideline-concordant care group — suggesting active monitoring did not result in a higher rate of invasive cancer than surgery at this early follow-up. European counterpart trials, LORD (Netherlands) and LORIS (UK), are also ongoing. Longer-term data from all these trials will be essential before active surveillance becomes a standard recommendation.

If you have been diagnosed with DCIS, discuss your grade, hormone receptor status, and options, including clinical trial participation, with your care team.

LCIS: A Related Condition

Lobular carcinoma in situ (LCIS) is a distinct finding that is generally not considered a cancer, but rather a biomarker of increased future risk. LCIS is typically discovered incidentally — found during biopsy performed for another reason — and does not form a detectable mass. Management focuses on surveillance and risk reduction (chemoprevention with tamoxifen or raloxifene), not surgery aimed at cure.

Inflammatory Breast Cancer (IBC): Rare but Aggressive

What Makes IBC Different?

Inflammatory breast cancer is a rare but particularly aggressive form of breast cancer, accounting for approximately 2–4% of breast cancer diagnoses in the United States, according to the National Cancer Institute. Despite its low incidence, IBC contributes to approximately 7% of breast cancer mortality, which is a reflection of how rapidly it can progress.

IBC is fundamentally different from other breast cancers in how it presents. It does not typically begin as a distinct lump. Instead, IBC develops when cancer cells block lymph vessels in the skin of the breast, causing the breast to become red, swollen, warm, and tender. A hallmark sign is peau d’orange — skin that develops a dimpled, orange-peel texture due to lymphatic obstruction. The affected breast may enlarge quickly, sometimes over a matter of days or weeks.

Because it mimics a breast infection (mastitis), IBC is frequently misdiagnosed initially. If you experience sudden, unexplained breast redness, swelling, or skin changes, particularly without fever or other signs of infection, or if antibiotic treatment does not resolve the symptoms, seek urgent evaluation from a breast specialist. IBC is classified as at least Stage IIIB at diagnosis, and it is always considered locally advanced or metastatic at presentation.

Racial disparities are pronounced: Black women have a substantially higher incidence of IBC than white women, according to published epidemiological data.

Treatment for IBC

Because of its aggressive nature, IBC is always treated with systemic therapy first, before surgery. Neoadjuvant chemotherapy — delivered prior to surgery — is the standard starting point. For HER2-positive IBC, HER2-targeted therapy (trastuzumab, pertuzumab) is added. For triple-negative IBC, pembrolizumab combined with chemotherapy has become part of the treatment landscape. Patients with BRCA mutations may also be eligible for PARP inhibitors.

After systemic therapy, surgery is performed — and for IBC, this means mastectomy; lumpectomy is not appropriate for IBC due to the diffuse nature of disease. Post-surgical radiation to the chest wall and regional lymph nodes follows. Outcomes for IBC have improved substantially over the past two decades with multimodal treatment, though it remains one of the most challenging subtypes.

Molecular Subtypes: ER, PR, HER2, and Beyond

Regardless of where a breast cancer originates anatomically, every invasive breast cancer is tested for three receptors. Understanding these receptor results — your biomarker profile — is essential to understanding your treatment plan.

Hormone Receptor-Positive (ER+ and/or PR+): “Luminal” Subtypes

Hormone receptor-positive breast cancer is the most common molecular category, accounting for approximately 70–80% of all breast cancers. These tumors express receptors for estrogen (ER), progesterone (PR), or both, meaning the hormones act as fuel for cancer cell growth. Blocking this hormonal signal is the cornerstone of treatment.

Luminal A tumors (ER-positive, PR-positive, HER2-negative, low Ki-67) are the most common subtype and carry the best overall prognosis. They are typically slow-growing, respond well to hormone therapy, and often do not require chemotherapy — particularly when genomic testing with Oncotype DX returns a low recurrence score. Luminal B tumors are hormone receptor-positive but more aggressive: they have a higher proliferation rate (higher Ki-67), may be HER2-positive, and more frequently require chemotherapy in addition to hormone therapy.

Standard hormone therapy includes tamoxifen (for premenopausal women) and aromatase inhibitors such as letrozole, anastrozole, or exemestane (for postmenopausal women). CDK4/6 inhibitors — abemaciclib, ribociclib, and palbociclib — have become a major advance in ER-positive breast cancer, significantly prolonging progression-free survival in the metastatic setting and reducing recurrence risk in high-risk early-stage disease.

HER2-Positive Breast Cancer

HER2 (human epidermal growth factor receptor 2) is a protein that promotes cell growth. In approximately 15–20% of breast cancers, the HER2 gene is amplified or the HER2 protein is overexpressed, causing cells to multiply faster than normal. Before targeted therapies existed, HER2-positive breast cancer was among the most feared diagnoses in oncology.

That landscape has changed dramatically. Trastuzumab (Herceptin), approved in 1998, was the first HER2-targeted therapy and transformed HER2-positive breast cancer from a high-risk subtype into one of the most treatable. Today the HER2-positive treatment toolkit includes pertuzumab, ado-trastuzumab emtansine (T-DM1), tucatinib, neratinib, lapatinib, margetuximab, and trastuzumab deruxtecan (T-DXd/Enhertu) — providing multiple lines of highly effective therapy.

A newly recognized and clinically important category is HER2-low. HER2-low breast cancer is defined as IHC 1+ or IHC 2+/ISH-negative — meaning HER2 is expressed at a low level that would previously have been classified as HER2-negative and thus ineligible for HER2-targeted therapy. In January 2025, the FDA approved T-DXd (Enhertu) for HR-positive, HER2-low or HER2-ultralow metastatic breast cancer based on results from the phase 3 DESTINY-Breast06 trial. In that trial, T-DXd reduced the risk of disease progression or death by 36–38% compared with physician’s choice of chemotherapy, with a median progression-free survival of 13.2 months versus 8.1 months. This approval meaningfully expands the population of patients who can benefit from HER2-directed therapy.

If your pathology report says “HER2 1+” or “HER2 2+ / ISH-negative,” ask your oncologist specifically about HER2-low-directed therapies.

Triple-Negative Breast Cancer (TNBC)

Triple-negative breast cancer is defined by what it lacks: ER-negative, PR-negative, and HER2-negative. Without hormonal or HER2 drivers to target, TNBC historically relied almost entirely on chemotherapy — which is effective but not precisely targeted. TNBC accounts for approximately 15% of breast cancers but disproportionately affects certain populations: younger women, women with germline BRCA1 mutations, and African American women, who are diagnosed with TNBC at roughly twice the rate of white women.

TNBC is more aggressive and has a higher recurrence risk than hormone receptor-positive breast cancer, particularly in the first three to five years after diagnosis. However, patients who remain disease-free at five years generally have a favorable long-term outlook, and the past decade has seen meaningful treatment advances.

Key developments in TNBC treatment include:

• Immunotherapy: Pembrolizumab (Keytruda), a PD-1 checkpoint inhibitor, is now approved in combination with chemotherapy for PD-L1-positive TNBC in the metastatic and early-stage settings. It is relevant for approximately 40% of patients with PD-L1-positive tumors.

• PARP inhibitors: For patients with germline BRCA1/2 mutations, olaparib and talazoparib exploit DNA repair defects in cancer cells. Adjuvant olaparib has been approved for high-risk, BRCA-mutated TNBC after chemotherapy and surgery.

• Antibody-drug conjugates: Sacituzumab govitecan (Trodelvy) delivers chemotherapy directly to cancer cells via a TROP-2 targeting antibody. Updated NCCN guidelines list sacituzumab govitecan as a Category 1 preferred first-line therapy for metastatic TNBC in patients without BRCA mutations. In 2025, data showed that sacituzumab govitecan combined with pembrolizumab reduced the risk of cancer progression by 35% compared with chemotherapy plus pembrolizumab in PD-L1-positive metastatic TNBC.

• Clinical trial landscape: TNBC has one of the most active clinical trial landscapes in breast oncology. If you have TNBC, exploring clinical trial eligibility is especially worthwhile.

Germline genetic testing (BRCA1, BRCA2, PALB2, and others) is recommended for all patients with TNBC, given the high prevalence of hereditary mutations in this population.

Less Common Types of Breast Cancer

Most breast cancers are IDC or ILC, but a smaller proportion fall into distinct histological categories that carry their own characteristics and prognoses.

Tubular carcinoma is a well-differentiated, low-grade form of invasive ductal carcinoma in which cancer cells form small, well-organized tube-like structures visible under the microscope. Tubular carcinomas are almost always ER-positive, grow slowly, and carry an excellent prognosis with very high long-term survival rates and a low risk of lymph node involvement.

Mucinous (colloid) carcinoma is characterized by cancer cells that produce abundant mucus, forming pools of mucin in which the tumor cells float. Mucinous carcinoma is typically ER-positive, slow-growing, and most common in older women. It carries a very favorable prognosis, particularly in its pure form (when mucin-producing cells predominate throughout the tumor).

Medullary carcinoma is an unusual histological subtype that, paradoxically, often has features associated with aggressive behavior (high-grade cells, high proliferation) but tends to behave more favorably than expected. Medullary carcinomas are frequently triple-negative by receptor testing, yet survival outcomes are often better than for other triple-negative tumors. They are associated with BRCA1 mutations.

Paget’s disease of the breast (also called Paget’s disease of the nipple) involves cancer cells in the skin of the nipple-areola complex. It typically presents as persistent crusting, scaling, or eczema-like changes of the nipple that do not respond to topical treatment. Paget’s disease of the breast is almost always associated with underlying DCIS or invasive breast cancer in the breast tissue beneath, which must be evaluated and treated. The condition represents less than 3% of breast cancer diagnoses.

Phyllodes tumors arise not from the epithelial cells lining the ducts and lobules, but from the connective (stromal) tissue of the breast. Most phyllodes tumors are benign, but a minority are borderline or malignant. Unlike most breast cancers, phyllodes tumors are typically ER-negative and do not respond to hormone therapy or standard chemotherapy. Treatment is surgical — wide local excision with clear margins — and malignant phyllodes tumors require close follow-up given their tendency to recur locally.

Why Your Breast Cancer Type Matters

Receptor status, histology, grade, and stage do not exist in isolation, but rather they combine to create your individual treatment roadmap. Consider two hypothetical patients, both diagnosed with Stage II breast cancer: a patient with Stage II HER2-positive ILC and a patient with Stage II Luminal A ER-positive IDC face entirely different systemic treatment plans, surgical considerations, and clinical trial options, despite sharing the same stage.

Understanding your specific subtype empowers you to ask better questions, advocate for appropriate testing, and make informed decisions alongside your care team. Some questions worth raising with your oncologist:

• What is my receptor status (ER, PR, HER2)? Is my HER2 score borderline — am I HER2-low?

• Has germline genetic testing, like BRCA, been recommended? (Especially relevant for TNBC and anyone with a family history)

• Is genomic testing such as Oncotype DX or Mammaprint appropriate for my case?

• What is my tumor grade and Ki-67 proliferation index?

• Based on my specific subtype, what clinical trials might I be eligible for?

Your breast cancer type also determines which stages are most relevant to your prognosis and which treatments are most appropriate. Ask your oncologist to walk you through your complete pathology report — every data point on it has implications for your care.

Understanding your breast cancer type is the first step toward finding the most effective treatment including clinical trials targeting your specific subtype. Ready to explore your options? Start your search with North’s trial finder.

Frequently Asked Questions

What is the most common type of breast cancer?

Invasive ductal carcinoma (IDC) is the most common type of breast cancer, accounting for approximately 70–80% of all invasive breast cancer diagnoses. IDC originates in the milk ducts and has broken through the duct wall into surrounding breast tissue. Within IDC, the molecular subtype (ER-positive, HER2-positive, triple-negative) varies and determines treatment.

What is the difference between invasive and non-invasive breast cancer?

Non-invasive breast cancer — primarily ductal carcinoma in situ (DCIS) — means abnormal cells are confined within the milk ducts and have not grown into surrounding breast tissue. Invasive breast cancer means cancer cells have broken through the duct or lobule wall and grown into adjacent tissue, where they potentially have access to lymphatic vessels and blood vessels. Invasive does not automatically mean the cancer has spread to other organs — it refers specifically to invasion of local breast tissue.

What is triple-negative breast cancer and why is it harder to treat?

Triple-negative breast cancer (TNBC) is defined by the absence of estrogen receptors, progesterone receptors, and HER2 overexpression. Because it lacks these specific targets, hormone therapies and HER2-targeted drugs — which are highly effective in other breast cancer subtypes — do not work for TNBC. Chemotherapy has historically been the primary systemic treatment. However, immunotherapy (pembrolizumab), PARP inhibitors (for BRCA-mutated TNBC), and antibody-drug conjugates (sacituzumab govitecan) have substantially broadened the treatment toolkit in recent years.

What is HER2-positive breast cancer?

HER2-positive breast cancer occurs when the HER2 gene is amplified or the HER2 protein is overexpressed, causing cancer cells to grow and divide more rapidly. It accounts for approximately 15–20% of breast cancers. While once considered a high-risk subtype, HER2-positive breast cancer is now one of the most treatable, thanks to targeted therapies including trastuzumab (Herceptin), pertuzumab, T-DM1, and trastuzumab deruxtecan (T-DXd/Enhertu). An expanded category called HER2-low is also now targetable with T-DXd, following FDA approval in January 2025.

Is DCIS the same as breast cancer?

DCIS (ductal carcinoma in situ) is classified as Stage 0 breast cancer by most oncology organizations because it consists of abnormal cells with cancer-like features that are confined to the milk ducts. A subset of DCIS cases would progress to invasive breast cancer if untreated. However, not all DCIS behaves the same way — low-grade DCIS carries a substantially lower progression risk than high-grade DCIS. With current treatment (surgery and, for ER-positive DCIS, hormone therapy), the prognosis is excellent. Active surveillance for select low-grade DCIS is being studied in clinical trials including COMET, LORIS, and LORD.

References

1. American Cancer Society. (2024). Breast Cancer Facts & Figures 2024–2025. https://www.cancer.org/content/dam/cancer-org/research/cancer-facts-and-statistics/breast-cancer-facts-and-figures/2024/breast-cancer-facts-and-figures-2024.pdf

2. Curigliano, G., et al. (2024). Trastuzumab Deruxtecan after Endocrine Therapy in Metastatic Breast Cancer (DESTINY-Breast06). New England Journal of Medicine. https://www.nejm.org/doi/abs/10.1056/NEJMoa2407086

3. Hwang, E. S., et al. (2024). Active Monitoring With or Without Endocrine Therapy for Low-Risk Ductal Carcinoma In Situ: The COMET Randomized Clinical Trial. JAMA. https://pubmed.ncbi.nlm.nih.gov/39665585/

4. Gradishar, W. J., et al. (2024). NCCN Clinical Practice Guidelines in Oncology: Breast Cancer. National Comprehensive Cancer Network. https://www.nccn.org/guidelines/guidelines-detail?category=1&id=1419

5. AstraZeneca US. (January 2025). ENHERTU approved in the US as first HER2-directed therapy for patients with HER2-low or HER2-ultralow metastatic breast cancer. https://www.astrazeneca-us.com/media/press-releases/2025/enhertu-fam-trastuzumab-deruxtecan-nxki-approved-in-the-us-as-first-her2-directed-therapy-for-patients-with-her2-low-or-her2-ultralow-metastatic-breast-cancer-following-disease-progression-after-one-or-more-endocrine-therapies.html

6. National Cancer Institute. (2024). Inflammatory Breast Cancer — StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK564324/

7. Breast Cancer Research Foundation. (2024). Understanding the Molecular Subtypes of Breast Cancer. https://www.bcrf.org/about-breast-cancer/molecular-subtypes-breast-cancer/

8. ASCO. (2025). Sacituzumab Govitecan Helps Some Patients With PD-L1-Positive Triple-Negative Breast Cancer Live Longer Without Cancer Progression. https://www.asco.org/about-asco/press-center/news-releases/sacituzumab-govitecan-helps-some-patients-with-PD-L1-positive-triple-negative-breast-cancer-live-longer-without-cancer-progression