5 Breast Cancer Advances in 2026—And The Questions They Leave Unanswered

Breast Cancer Awareness Month arrives amid a consequential year for treatment. FDA decisions have expanded antibody-drug conjugates (ADCs) into earlier settings and expanded options for patients whose tumors develop endocrine resistance. These changes give clinicians more opportunities to intervene, but an approval does not resolve every question about how a treatment should fit into care.^1-5

For pharmacists, the next step is translating new evidence into decisions that account for prior therapy and the patient’s ability to tolerate treatment. Five developments illustrate where breast cancer care is advancing—and where evidence still needs to catch up.

1. Earlier HER2-Directed ADC Treatment: How Much Benefit Is Established?

On May 15, 2026, the FDA approved fam-trastuzumab deruxtecan-nxki (T-DXd, Enhertu; Daiichi Sankyo) for 2 HER2-positive early-stage breast cancer settings: neoadjuvant treatment followed by taxane, trastuzumab, and pertuzumab for stage II or III disease, and adjuvant treatment for residual invasive disease after trastuzumab- and taxane-based neoadjuvant therapy.¹

In DESTINY-Breast05 (NCT04622319), 3-year invasive disease-free survival was 92.4% with T-DXd versus 83.7% with trastuzumab emtansine (hazard ratio [HR], 0.47; 95% CI, 0.34-0.66). In DESTINY-Breast11 (NCT05113251), the neoadjuvant regimen improved pathological complete response, but event-free and overall survival end points were not statistically controlled or powered.¹

The question is how those distinct evidence bases should inform treatment discussions. Pharmacists should explain the demonstrated benefit for each setting while reinforcing prompt reporting of respiratory symptoms because T-DXd carries a boxed warning for interstitial lung disease and pneumonitis.¹

2. Dato-DXd in TNBC: Which Patients Should Receive It First?

On May 22, 2026, datopotamab deruxtecan-dlnk (Dato-DXd, Datroway; Daiichi Sankyo) gained approval for unresectable or metastatic triple-negative breast cancer (TNBC) in adults who are not candidates for PD-1/PD-L1 inhibitor therapy.²

TROPION-Breast02 enrolled patients without prior systemic treatment for advanced disease. Median progression-free survival (PFS) was 10.8 months with Dato-DXd versus 5.6 months with chemotherapy (HR, 0.57; 95% CI, 0.47-0.69). Median overall survival was 23.7 vs 18.7 months (HR, 0.79; 95% CI, 0.64-0.98).²

The unresolved decision is how to choose among available ADCs for patients eligible for more than one option. This trial compared Dato-DXd with chemotherapy, not another ADC. Pharmacists can help assess suitability by reviewing pulmonary history and preparing patients for ocular adverse reactions and stomatitis.²

3. Sacituzumab Moves Forward: What Comes After First-Line ADC Therapy?

On June 24, 2026, multiple approvals expanded sacituzumab govitecan-hziy (Trodelvy; Gilead Sciences) into first-line for unresectable locally advanced or metastatic TNBC, alone for patients ineligible for PD-1/PD-L1 inhibitor therapy or with pembrolizumab (Keytruda, Merck & Co.)-based treatment for tumors with a PD-L1 combined positive score of at least 10.³

Median PFS improved to 9.7 vs 6.9 months with monotherapy in ASCENT-03 (NCT05382299) and to 11.2 vs 7.8 months with the pembrolizumab combination in ASCENT-04/KEYNOTE-D19 (NCT05382286). Overall survival data were immature in both studies.³

Neither comparison establishes the best treatment after progression on first-line sacituzumab. Pharmacists should avoid assuming that another ADC will reproduce benefits observed in a different population. Immediate implementation also requires attention to sacituzumab’s boxed warnings for diarrhea and neutropenia, with immune-mediated toxicity assessment when pembrolizumab is included.³

4. More Intensive Maintenance: Will Longer Disease Control Improve Survival?

Also on June 24, 2026, palbociclib (Ibrance; Pfizer) received approval with trastuzumab, with or without pertuzumab, and endocrine therapy as maintenance after induction treatment for HR-positive, HER2-positive, locally advanced, or metastatic breast cancer.⁴

PATINA (NCT02947685) demonstrated improved PFS with palbociclib (HR, 0.76; 95% CI, 0.59-0.97), although overall survival data were immature. The FDA reported that median PFS could not be adequately described because of censoring.⁴

Whether improved disease control translates into longer survival remains unanswered. Adding an oral agent also makes maintenance more demanding. Pharmacists can help patients manage the 21-day on, 7-day off schedule and reinforce monitoring for neutropenia, a labeled warning.⁴

5. Switching Before Imaging Progression: Does Earlier Mean Better?

On September 4, 2026, camizestrant (Etcamah; AstraZeneca) received accelerated approval with a CDK4/6 inhibitor for HR-positive, HER2-negative advanced breast cancer upon detection of an ESR1 mutation during aromatase inhibitor–CDK4/6 inhibitor therapy using an FDA-authorized test.⁵

This introduces a treatment switch guided by circulating tumor DNA before imaging demonstrates progression. Estimated median PFS was 16 months after switching versus 9.2 months with continued aromatase inhibitor treatment.⁵

The central question remains whether intervening at molecular resistance rather than confirmed progression provides clinically meaningful benefit; the FDA requires confirmatory studies. Pharmacists must also review interacting medications because camizestrant carries a boxed warning for irregular heart rhythm with certain concomitant drugs. This advance makes careful interpretation of the evidence as important as access to the treatment itself.⁵

REFERENCES

1. FDA approves two separate indications for fam-trastuzumab deruxtecan-nxki in HER2-positive early-stage breast cancer. FDA. May 16, 2026. Accessed October 16, 2026. https://www.fda.gov/drugs/resources-information-approved-drugs/fda-approves-two-separate-indications-fam-trastuzumab-deruxtecan-nxki-her2-positive-early-stage

2. FDA approves datopotamab deruxtecan-dlnk for unresectable or metastatic triple-negative breast cancer. FDA. May 22, 2026. Accessed October 16, 2026. https://www.fda.gov/drugs/resources-information-approved-drugs/fda-approves-datopotamab-deruxtecan-dlnk-unresectable-or-metastatic-triple-negative-breast-cancer

3. FDA approves sacituzumab govitecan-hziy as monotherapy and in combination with pembrolizumab for first-line treatment of triple-negative breast cancer. FDA. June 24, 2026. Accessed October 16, 2026. https://www.fda.gov/drugs/resources-information-approved-drugs/fda-approves-sacituzumab-govitecan-hziy-monotherapy-and-combination-pembrolizumab-first-line

4. FDA approves palbociclib with trastuzumab, with or without pertuzumab, and endocrine therapy for the maintenance treatment of HR-positive, HER2-positive metastatic breast cancer. FDA. June 24, 2026. Accessed October 16, 2026. https://www.fda.gov/drugs/resources-information-approved-drugs/fda-approves-palbociclib-trastuzumab-or-without-pertuzumab-and-endocrine-therapy-maintenance

5. FDA grants accelerated approval to a new breast cancer treatment. FDA. September 4, 2026. Accessed October 16, 2026. https://www.fda.gov/news-events/press-announcements/fda-grants-accelerated-approval-new-breast-cancer-treatment