This weekly update brings you the latest in breast cancer guidelines and research from the past week. We summarize guidelines and highlight key points to help patients, caregivers, and health care professionals stay current with this dynamic, evolving field. Note that both U.S. and international guidelines and research are included, so that we are inclusive of both domestic and international audiences.

The week’s top guidelines and research:

1. Breast Cancer, Version 5.2025 — Featured Updates to the NCCN Guidelines
These updated guidelines reflect how breast cancer treatment is becoming less invasive without compromising safety. More patients can safely avoid full removal of axillary lymph nodes thanks to new studies showing no added benefit. Radiation strategies are also becoming simpler and shorter, including options for women undergoing reconstructive surgery. The guidelines now also better define which patients can receive partial breast irradiation instead of whole-breast treatment.

Key message:
• Safer, less invasive treatment options are now validated for more patients.

Reference: JNCCN, 2025 — Read here

2. VENUSCANCER: Global Variation Patterns in Breast Cancer
This large-scale international analysis evaluated global patterns in breast cancer epidemiology, tumor biology, and outcomes. It identified substantial regional disparities in age at diagnosis, subtype distribution, and stage. This international study highlights major differences in how quickly patients around the world receive breast cancer care. Some countries can operate within weeks, while others see delays of many months to a full year. These delays often reflect broader challenges in healthcare systems, not patient factors. Earlier diagnosis and faster treatment consistently improve survival, making these findings highly relevant for global health planning.

Key message:
• Time to treatment varies dramatically worldwide and affects outcomes.

Reference: The Lancet Oncology, 2025 — Read here

3. Trastuzumab Deruxtecan (T-DXd) Resistance via Loss of HER2 Expression and Binding
Researchers examined why some tumors stop responding to T-DXd, a very effective HER2-targeted therapy. They found that many tumors simply lose HER2 over time, making the drug less able to bind and deliver its chemotherapy payload. Other tumors develop mutations that prevent the drug from attaching properly.

Key message:
• Tumors can “escape” HER2 therapies by losing HER2 itself.

Reference: Cancer Discovery, 2025 — Read here

4. Association of Neoadjuvant Chemotherapy Dose Intensity with Pathological Complete Response and Event-Free Survival in HER2-Negative Early Breast Cancer
This study shows that receiving the full planned intensity of chemotherapy before surgery matters, especially for triple-negative breast cancer. Patients who maintained at least 85% of the recommended dose had higher chances of fully eliminating the tumor and better long-term outcomes. Even small reductions or delays may lower effectiveness.

Key messages:
• Staying as close as possible to full chemo dose improves results.
• Dose reductions should be avoided unless medically necessary.

Reference: European Journal of Cancer, 2025 — Read here

5. Multi-Cellular Phenotypic Dynamics During the Progression of an Immunocompetent Breast Cancer Model
This study looked at longitudinal single-cell RNA-seq (mouse model) mapping for the temporal evolution of tumor ecosystems. Tumors were harvested at 4 predefined time points and scRNAsew was performed. Using advanced single-cell technology, scientists followed how tumors evolve over time in a living immune system. As cancers grow, they become more skilled at avoiding immune attacks. Immune cells, like macrophages and T cells, initially respond strongly but weaken as the tumor adapts.

Key messages:
• Tumors change in predictable ways as they evade the immune system.
• Timing may be crucial for effective immunotherapy.

Reference: Cell (iScience), 2025 — Read here

6. The Tumor Microenvironment of 14,837 Breast Cancers Is Associated with Clinical Outcome Independently of Genomic Subtypes
This huge study shows that the tissue surrounding the tumor (the microenvironment) is just as important as the cancer cells themselves. Some tumors are surrounded by active immune cells, while others have very few, which affects long-term outcomes. Even patients with the same tumor subtype can have very different microenvironments, and very different prognosis. These findings could lead to new biomarkers that better personalize treatment.

Key message:
• The microenvironment can strongly predict outcomes beyond tumor genomics.

Reference: Cell Reports Medicine, 2025 — Read here

7. Cardiotoxic Effects of Antibody-Drug Conjugates vs Standard Chemotherapy in ERBB2-Positive Advanced Breast Cancer
This analysis compared the heart-related side effects of different HER2-targeted treatments. T-DM1 showed the lowest rate of heart weakening, making it one of the safest HER2 therapies for the heart. T-DXd and trastuzumab-based combinations had similar risks, though still generally low. These findings reassure patients but also highlight the importance of regular heart monitoring during treatment.

Key message:
• T-DM1 is the safest HER2 therapy for the heart and heart monitoring remains important with T-DXd.

Reference: JAMA Network Open, 2025 — Read here