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Oral Therapy HRpos HER2neg BC
Q&A on Oral Targeted Therapies in HR+/HER2- Breast Cancer for Oncology Pharmacists

Released: July 28, 2026

Jordan Hill
Jordan Hill, PharmD, BCOP
Danielle Roman
Danielle Roman, PharmD, BCOP
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Key Takeaways
  • Biomarker testing should be timed to the treatment decision. ESR1 testing is most informative at progression on endocrine therapy, and a negative plasma result should be interpreted in the context of ctDNA shedding and the estimated tumor fraction.
  • Proactive regimen-specific prevention, early follow-up, and timely dose modification are central to treatment persistence.

In this commentary, Danielle Roman, PharmD, BCOP, and Jordan Hill, PharmD, BCOP, address practical questions raised during the live symposium, “Advances in Oral Targeted Therapies for HR+/HER2- Breast Cancer: Best Practices for Oncology Pharmacists.” They discuss sequencing adjuvant targeted therapies, timing and interpreting biomarker testing, selecting PI3K/AKT pathway regimens, preventing and managing adverse events, and using dose modification to support treatment persistence.

If your patient with high-risk, germline BRCA1/2-mutated, hormone receptor (HR)–positive/HER2-negative early breast cancer is eligible for both adjuvant olaparib and a CDK4/6 inhibitor, how do you decide between them or, if you use both, how do you sequence them?

Danielle Roman, PharmD, BCOP:
This is a genuine clinical gray area because the pivotal trials (OlympiA for olaparib; monarchE and NATALEE for the adjuvant CDK4/6 inhibitors) did not evaluate these agents together or in a planned sequence. I would first confirm that the patient clearly meets the eligibility criteria for the individual therapies. For olaparib, that means a pathogenic or likely pathogenic germline BRCA1/2 variant, HER2-negative early breast cancer, and the high-risk features included in OlympiA. For abemaciclib or ribociclib, I would confirm that the patient meets the criteria for the FDA-approved indication and review the expected treatment duration and toxicity profile.

When a motivated patient is an appropriate candidate for both approaches, my preference would be to avoid concurrent administration because efficacy and safety have not been established and overlapping hematologic and gastrointestinal toxicities could make treatment difficult to complete. Sequential therapy may be considered, with a practical approach being completing 1 year of olaparib and then considering a CDK4/6 inhibitor. However, this is an extrapolated strategy rather than a trial-proven standard, and the timing may fall outside the treatment initiation windows used in the pivotal CDK4/6 inhibitor trials. Such uncertainty should be discussed explicitly with the patient and the multidisciplinary team. If sequential use is considered, I would document the rationale, confirm that the second therapy remains clinically appropriate at its planned start, and reassess tolerance, treatment burden, and the patient’s priorities before initiating it.

Jordan Hill, PharmD, BCOP:
I agree that there is no single correct answer. I would weigh the magnitude and type of recurrence risk, including residual disease, nodal burden, grade, tumor size, prior chemotherapy, and the patient’s overall health. I would also assess baseline blood counts, renal and hepatic function, gastrointestinal history, concomitant medications, the patient’s ability to complete prolonged oral therapy, access, and personal goals. For some patients, the cumulative burden of endocrine therapy (ET) plus multiple years of targeted therapy may ultimately drive the decision. The pharmacist can help the team compare monitoring requirements, anticipate overlapping toxicities, and ensure that the patient understands where evidence ends and clinical judgment begins.

When should biomarker testing be performed or repeated in HR-positive/HER2-negative metastatic breast cancer, and what do you do if a plasma-based assay is negative, circulating tumor (ct)DNA levels are low, or the patient has bone-only disease?

Jordan Hill, PharmD, BCOP:
The timing of testing should match the biology of the alteration and the treatment decision. Acquired ESR1 mutations commonly emerge under the selective pressure of aromatase inhibitor therapy, so ESR1 mutation testing should be performed at recurrence or progression. Plasma ctDNA is often preferred because it can capture heterogeneity across metastatic sites while avoiding an invasive tissue biopsy. By contrast, a nonacquired alteration such as PIK3CA may be detectable in archival tissue, although a current metastatic specimen or ctDNA result can be helpful when available.

A negative plasma result does not necessarily exclude the presence of the alteration in tumor tissue. Patients with bone-only disease, low-volume disease, or otherwise low ctDNA shedding may have an uninformative plasma test. I would review whether the report includes a tumor fraction estimate or evidence that ctDNA was present. If the sample appears to have low tumor fraction, I would consider repeating ctDNA testing at a clinically appropriate time or obtaining tumor tissue if the result could influence treatment selection. Bone biopsies may be challenging for molecular testing because decalcification can compromise nucleic acid quality, so coordination with pathology before specimen collection is important.

Danielle Roman, PharmD, BCOP:
From a workflow perspective, one of the most important pharmacist roles is making sure the test is ordered early enough to inform the next treatment decision and that the results are reviewed and acted upon. I would build a process that records the specimen type, collection date, assay, tumor fraction when reported, actionable findings, and the treatment options linked to those findings. A negative or inconclusive result should prompt a discussion rather than automatically closing the testing pathway. This has become even more important because elacestrant, imlunestrant, and vepdegestrant are approved options for appropriately selected patients with ER-positive/HER2-negative, ESR1-mutated advanced or metastatic disease after progression following ≥1 line of ET. Recent SERENA-6 data also highlight the clinical value of serial ctDNA monitoring to detect emerging ESR1 mutations and support switching the endocrine backbone before radiographic progression. However, camizestrant remains investigational in the United States, so switching therapy before radiographic progression should not be presented as routine standard care outside a clinical trial or defined protocol.

For a patient with PIK3CA-mutated, HR-positive/HER2-negative advanced breast cancer, how does the timing and context of recurrence help distinguish a patient who may be appropriate for inavolisib plus palbociclib and fulvestrant from one who may be better suited for capivasertib plus fulvestrant?

Jordan Hill, PharmD, BCOP:
The most important distinction is the clinical setting represented in the pivotal trials and approved indications. The inavolisib triplet is most directly aligned with endocrine-resistant disease that recurs during adjuvant ET or soon after its completion. INAVO120 enrolled patients whose disease recurred or progressed during or within 12 months after completion of adjuvant ET and who had not received prior systemic therapy for advanced disease. In this early-relapse setting, the triplet regimen simultaneously targets PIK3CA-mutated signaling and incorporates CDK4/6 inhibition as part of first-line therapy for advanced disease.

Capivasertib plus fulvestrant, as studied in CAPItello-291, is positioned after progression on ≥1 endocrine-based regimen in the metastatic setting or recurrence on or within 12 months of completing adjuvant therapy for tumors with ≥1 qualifying PIK3CA, AKT1, or PTEN alteration. In practice, it is commonly considered after progression on first-line CDK4/6 inhibitor plus ET. The 2 regimens should not be treated as interchangeable simply because both act on the PI3K/AKT pathway. Recent VIKTORIA-1 results led to FDA approval of intravenous gedatolisib with fulvestrant, with or without palbociclib, for adults with HR-positive/HER2-negative locally advanced or metastatic breast cancer without a detected PIK3CA mutation following progression on or after at least 1 line of ET in the metastatic setting. Because the approved indication is limited to disease without a detected PIK3CA mutation, this regimen would not apply to the PIK3CA-mutated patient described here, but it broadens pathway-directed options for other patients.

Danielle Roman, PharmD, BCOP:
After confirming the PIK3CA mutation and HR-positive/HER2-negative disease, I would individualize the choice around comorbidities and regimen burden. For the inavolisib triplet, I pay close attention to baseline glucose levels, oral health, stomatitis risk, and bone marrow reserve, particularly because palbociclib contributes substantially to the risk of neutropenia. For capivasertib, I focus on diarrhea, rash, hyperglycemia, and the patient’s ability to follow a schedule of 4 days on/3 days off. Prior therapy, endocrine sensitivity, disease tempo, organ function, medication interactions, access, and the patient’s preference for regimen complexity all matter.

What should a pharmacist-led pretreatment and early monitoring plan include for a patient starting a PI3K- or AKT-pathway regimen, and how should that plan be individualized to prevent or rapidly manage hyperglycemia, rash, stomatitis, and diarrhea?

Danielle Roman, PharmD, BCOP:
The plan should begin before the first dose. I review fasting plasma glucose and A1C, diabetes history and current antihyperglycemic therapy, baseline bowel habits, oral health, dermatologic and allergy history. I also obtain a comprehensive metabolic panel to assess renal and hepatic function and electrolytes, with particular attention to renal function before initiating inavolisib, as well as a complete blood count (CBC) when relevant. In addition, I assess the patient’s ability to follow the dosing schedule, and confirm access to supportive medications, home glucose monitoring when appropriate, and timely follow-up.

I use a written action plan that explains what to monitor, what to start at the first sign of toxicity, when to contact the oncology team, and when the anticancer agent should be held. Teach-back is especially helpful with intermittent regimens. My practical priorities differ by agent. For inavolisib plus palbociclib and fulvestrant, I focus on early glucose monitoring, stomatitis prevention and oral care, and CBC monitoring for palbociclib-associated neutropenia. For capivasertib plus fulvestrant, I provide a clear 4-days-on/3-days-off calendar, establish plans for prompt management of diarrhea and rash, and monitor glucose based on the prescribing information. For alpelisib plus fulvestrant, I pay particularly close attention to baseline metabolic risk and rash prevention. For hyperglycemia specifically, prophylactic metformin has prospective evidence with alpelisib (METALLICA trial), but its use should be individualized because metformin can add gastrointestinal toxicity, and the evidence should not be assumed to apply equally to other pathway inhibitors. For gedatolisib-based therapy, I would follow the current prescribing information. Gedatolisib is administered as a 180-mg intravenous infusion over 30 minutes on Days 1, 8, and 15 of each 28-day cycle with fulvestrant, with or without palbociclib. I would coordinate the infusion schedule and monitor proactively for stomatitis, dermatologic adverse reactions, and hyperglycemia, using the label-recommended treatment interruption and dose-modification guidance when needed.

For rash prevention or early management, I may consider a nonsedating oral antihistamine when appropriate. Fexofenadine is a reasonable alternative to cetirizine, particularly if sedation is a concern. The choice can be individualized according to prior response, comorbidities, drug interactions, cost, and access. The strongest evidence for antihistamine prophylaxis comes from alpelisib studies, so I would not assume the same benefit across every PI3K or AKT pathway regimen.

Jordan Hill, PharmD, BCOP:
Early follow-up is as important as the baseline plan. I would contact the patient within the first 1-2 weeks, or sooner if baseline metabolic or gastrointestinal risk is high, and ask specifically about thirst, urination, oral pain, food intake, stool frequency, rash, and adherence to the dosing calendar. Patients should know that the goal is to identify and address toxicities before they become severe. Supportive therapy, treatment interruption, or dose adjustment can be used early to preserve long-term treatment.

When adverse events emerge during adjuvant abemaciclib or ribociclib, how do you decide among supportive care, treatment interruption, dose reduction, and permanent discontinuation, and how do you explain dose reduction to a patient who fears that a lower dose will reduce treatment efficacy?

Danielle Roman, PharmD, BCOP:
I start by consulting the agent-specific prescribing information and assessing the severity, duration, and recurrence of the toxicity. With abemaciclib, early diarrhea can often be managed with prompt antidiarrheal therapy, increased oral fluid intake, dietary changes as appropriate, and close follow-up. Persistent grade 2 or grade 3 or 4 diarrhea requires interruption, and recurrent or severe events generally warrant dose reduction. With ribociclib, neutropenia, hepatotoxicity, and QT prolongation each have distinct thresholds for holding, reducing, or permanently discontinuing treatment. Because ribociclib has different starting doses and dose reduction levels in early-stage and advanced or metastatic breast cancer, pharmacists should apply the correct indication-specific dosing pathway when managing toxicities.

The key is to intervene before toxicity causes the patient to stop treatment on their own. I explain that a temporary hold or dose reduction is a planned tool for keeping the patient on therapy safely. It is not a sign that the treatment has failed. I also give the patient a clear follow-up plan so they know when labs will be repeated, when symptoms should improve, and whether treatment will resume at the same or a reduced dose. I often tell patients, “A dose adjustment is not a failure. It is one of the ways we manage side effects so you can continue treatment safely. The clinical trials allowed dose holds and reductions, and patients continued to benefit. We will monitor you closely and use the highest dose that remains safe and tolerable for you.”

Jordan Hill, PharmD, BCOP:
The exploratory monarchE and NATALEE analyses of CDK4/6 inhibitor dose modification are reassuring because patients who required protocol-guided dose reductions continued to derive treatment benefit. Those analyses do not prove that every lower dose is equivalent for every patient, but they support using the approved dose modification pathways rather than allowing manageable toxicity to cause premature discontinuation. I frame the conversation around the treatment goal: the best dose is the dose the patient can safely continue for the intended duration.

The phase II TRADE study also showed that a step-up strategy with abemaciclib allowed many patients to reach and maintain the target dose, with low early discontinuation (6.7%). This approach is promising and may be considered in selected patients, but it differs from the FDA-approved starting dose and remains an investigational dosing strategy. It should be implemented only through a defined institutional approach with appropriate counseling and monitoring.

Your Thoughts
Which challenge most often limits your ability to keep patients on treatment with newer targeted therapies for HR-positive/HER2-negative breast cancer? What workflows, counseling approaches, or supportive care strategies have worked well in your practice?

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How often do you check in with your patients within 1-2 weeks of starting a new oral medication regimen for their HR-positive/HER2-negative breast cancer?

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