Anthracycline-Free Neoadjuvant Pertuzumab-Trastuzumab-Taxane in Patients with HER2-Positive Early Breast Cancer: Hormone Receptor Status as a Key Determinant of Pathological Complete Response.

1. Introduction
Neoadjuvant chemotherapy is a key component of treatment for early breast cancer (EBC), particularly in HER2-positive tumors, where it allows both local disease control and early eradication of micrometastases. Pathological complete response (pCR), defined as the absence of residual invasive disease in the breast and axillary lymph nodes (ypT0/is ypN0), is recognized as an important prognostic marker, especially in the HER2-positive and triple-negative settings. The CTNeoBC pooled analysis of more than 12,000 patients showed a strong association between pCR and long-term clinical benefit, while leaving open the debate on the value of pCR as a definitive surrogate endpoint for event-free survival (EFS) and overall survival (OS) [1].
The most recent international guidelines, including the 2024 ESMO recommendations, support neoadjuvant treatment with 6–8 cycles of chemotherapy combined with dual anti-HER2 blockade (trastuzumab plus pertuzumab) in patients with tumors clinically ≥cT2 and/or node-positive disease (≥cN1), with progressive extension of this approach to smaller, high-risk tumors (cT1c). Pivotal studies established this standard: the NOAH trial showed that adding trastuzumab to neoadjuvant chemotherapy doubled the pCR rate (from 19% to 38%) and significantly improved EFS, while subsequent escalation strategies testing various single- or dual-HER2 blockade combinations, demonstrated progressive improvements in pCR rates and survival outcomes [2].
Dual HER2 blockade with pertuzumab and trastuzumab combined with taxane-based chemotherapy has become the standard neoadjuvant approach for HER2-positive EBC, with pCR rates strongly influenced by hormone receptor (HR) status: median pCR rates of approximately 45% in HR-positive/HER2-positive tumors versus 70% in HR-negative/HER2-positive disease [3]. The NeoSphere trial [4,5] demonstrated that adding pertuzumab to trastuzumab plus docetaxel increases pCR rates from 29% to 46%, with a 5-year benefit in EFS. Subsequent trials (TRYPHAENA [6], TRAIN-2 [7], KRISTINE [8], NEOPETRA [9], GeparSepto [10]) and real-world studies (BrUOG [11], NEOPERSUR [12]) have consistently shown that anthracycline-free regimens combining dual HER2 blockade with taxanes achieve pCR rates of 60–70% in HR-negative disease and 45–50% in HR-positive disease, with significantly reduced hematological and cardiac toxicity compared with anthracycline-containing regimens. De-escalation strategies (WSG-ADAPT [13], neoCARHP [14], CompassHER2 pCR [15], PHERGain [16]) have further demonstrated that chemotherapy intensity can be reduced while maintaining high pCR rates and excellent survival outcomes, particularly in HR-negative patients.
In parallel, the role of PIK3CA mutations in HER2-positive tumors has emerged as an important but still controversial biological factor. PIK3CA mutations, present in approximately 20% of HER2-positive BCs—particularly in hotspot regions in exons 9 and 20—have been associated in several studies with lower pCR rates under anti-HER2 therapy, especially in HR-positive tumors, suggesting a potential role in partial resistance to HER2 blockade. However, the impact of these mutations on DFS and OS appears less clear, with inconsistent results across different series. Recent analyses in large prospective cohorts have confirmed the association between PIK3CA mutations and a lower likelihood of achieving pCR, but without a consistent worsening of long-term outcomes across all populations [17,18,19,20].
In this context of highly effective dual HER2 blockade with taxanes, progressive chemotherapy de-escalation and increasing attention to biomarker-driven personalization, it remains unclear whether, in HER2-positive tumors treated with modern neoadjuvant regimens (often anthracycline-free), PIK3CA mutations still exert an adverse effect on pCR and survival outcomes, and how this impact is modulated by HR status. The present study addresses this question by evaluating, in a real-world cohort treated with pertuzumab–trastuzumab–taxane (THP), the interplay between HR status, PIK3CA mutations, pCR rates, early survival outcomes and toxicity profile, with the aim of informing more effective and potentially de-escalated treatment strategies for HER2-positive EBC.

2. Materials and Methods

2.1. Study Population
This observational study, with a median follow-up of 42 months, aimed to evaluate the efficacy and safety of the THP regimen in patients with stage II–III HER2-positive BC.
Between April 2017 and March 2021, 56 consecutive patients with EBC completed pre-planned neoadjuvant systemic therapy followed by definitive breast surgery at the Medical Oncology Unit of San Salvatore Hospital, University of L’Aquila (Italy).
Eligibility criteria included: age ≥18 years; histologically confirmed HER2-positive BC, defined as IHC 3+ or IHC 2+ with FISH amplification according to local diagnostic procedures; early-stage disease treated with six cycles of pertuzumab (loading dose 840 mg, then 420 mg) and trastuzumab (loading dose 8 mg/kg, then 6 mg/kg) in combination with docetaxel (75 mg/m2) every 21 days.
Tumor response to neoadjuvant therapy was assessed using standardized imaging, including baseline ultrasound and reassessment every three cycles, plus mammography and/or magnetic resonance imaging at baseline and at the end of treatment.
Surgery was performed 3–6 weeks after the last cycle of neoadjuvant therapy.
The primary endpoint was the total pCR rate, defined as the absence of residual invasive disease in the breast and lymph nodes (ypT0/is ypN0), independently assessed by two experienced pathologists at the center.
Secondary endpoints included the incidence and severity of treatment-related adverse events (AEs), prospectively recorded according to NCI-CTC version 5, and graded as 1–2 or 3–4. Safety monitoring comprised routine laboratory tests at each cycle, including serial measurements of cardiac biomarkers (troponin I and NT-proBNP), as well as echocardiographic and electrocardiographic assessments every three cycles.
An exploratory ancillary analysis was performed to investigate the association between treatment efficacy and PIK3CA mutational status, evaluated on diagnostic biopsy samples available in a subgroup of 36 patients.
All living participants provided informed consent at the time of data collection. The study was conducted in accordance with Good Clinical Practice and the ethical principles of the Declaration of Helsinki and was approved by the local Ethics Committee of the L’Aquila center (protocol 32865/2018). Data collection was completed in December 2025.

2.2. PIK3CA Genotyping
PIK3CA genotyping was performed using an allele-specific real-time PCR assay. DNA was extracted from formalin-fixed paraffin-embedded (FFPE) tissue samples with the Zymo Quick DNA FFPE Kit (Zymo Research, Irvine, CA, USA), strictly following the manufacturer’s instructions.
Subsequently, mutational analysis was carried out using the EasyPGX PIK3CA kit (Diatech Pharmacogenetics, Jesi, Italy), a CE-IVD-certified assay, according to the manufacturer’s protocol. These highly sensitive assays, with limits of detection between 0.5% and 2%, enabled identification of approximately 90% of the known PIK3CA variants described in BC, based on data from the COSMIC database (Wellcome Sanger Institute, Hinxton, UK; accessed 12 December 2021). The analyses targeted specific hotspot regions in exons 4, 7, 9 and 20.
DNA quality and quantity were assessed using spectrophotometric measurements, and samples with DNA concentration < 10 ng/µL or A260/A280 ratio outside the range of 1.8–2.0 were excluded from further analysis. Only samples with adequate DNA integrity and purity were included in the PIK3CA mutational analysis to ensure reliability of the results.

2.3. Statistical Analysis
Baseline patient characteristics were summarized using descriptive statistics (means, medians, and proportions), and categorical variables were compared between groups using the chi-square test or Fisher’s exact test, as appropriate.
To identify independent predictors of pCR, we fitted a multivariable logistic regression model including HR status, tumor grade (2 vs. 3), and Ki-67 proliferation index (<20% vs. ≥20%) as covariates, selected based on clinical relevance and univariate associations with pCR. Additional clinical and pathological variables (age, menopausal status, and clinical T and N stage) were explored in an extended model but were not retained in the final parsimonious model because they were not statistically significant and their inclusion risked overfitting given the limited sample size (56 patients, 34 pCR events). PIK3CA mutational status was not included in the primary model because testing was available in only 36 patients (64% of the cohort); instead, an exploratory model including PIK3CA was fitted in this subset. Odds ratios (ORs) and 95% confidence intervals (CIs) were reported, and a two-sided p-value < 0.05 was considered statistically significant. All analyses were performed using Python (version 3.x; Python Software Foundation, Wilmington, DE, USA) with the statsmodels library (version 0.14). Given the exploratory nature of the study and the modest cohort size (n = 56 overall; n = 36 with PIK3CA testing, including only 8 mutated cases), no formal sample size calculation was performed. The study was not powered to detect statistically significant differences in pCR rates by PIK3CA status, and all analyses related to PIK3CA mutations should be regarded as hypothesis-generating. Post hoc power calculations indicated that, with eight mutated cases, the study had <20% power to detect a 20-percentage-point difference in pCR rates between PIK3CA-mutated and wild-type tumors at a two-sided α of 0.05; therefore, the absence of a statistically significant association between PIK3CA status and pCR in this cohort should not be interpreted as evidence of no effect, and larger prospective studies are needed to clarify this relationship.

3. Results

3.1. Patient Characteristics
Baseline patient characteristics are summarized in Table 1. The cohort included 21 patients (37.5%) with HR-negative and 35 (62.5%) with HR-positive HER2-positive EBC, with a median age of 54 years (range 28–79). Most patients had ECOG performance status 0 and low comorbidity burden, and the majority presented with T2–T4 and node-positive disease, reflecting a predominantly locally advanced population. Histologically, invasive ductal carcinoma and high Ki-67 (≥20%) were predominant. No statistically significant differences in baseline characteristics were observed between HR-negative and HR-positive groups (all p > 0.05).

3.2. Primary Endpoint: Pathological Complete Response
Overall, 34 of 56 patients achieved pCR, corresponding to a rate of 60.7% (ypT0/is ypN0), consistent with major clinical trials evaluating dual HER2 blockade combined with taxane-based neoadjuvant chemotherapy.
In this cohort, HR status emerged as the main clinical predictor of pCR (Table 2).
HR-negative patients achieved a pCR rate of 85.7% compared with 45.7% in HR-positive patients (p = 0.007, chi-square test; odds ratio 7.125, 95% CI 1.87–27.15), corresponding to an approximately seven-fold higher likelihood of pCR and a 40-percentage-point absolute difference.
Among the 36 patients with available PIK3CA testing, 28 (77.8%) were wild-type and eight (22.2%) harbored a PIK3CA mutation. No statistically significant association between PIK3CA status and pCR was observed (Table 3): pCR rates were 60.7% in wild-type tumors and 62.5% in mutated tumors (p = 1.000, Fisher’s exact test), but this exploratory analysis was limited by the small number of mutated cases and should be considered hypothesis-generating rather than definitive.
Stratified analysis according to HR and PIK3CA status (Table 4) confirmed HR status as the predominant factor associated with pCR in this cohort. HR-negative patients achieved high pCR rates irrespective of PIK3CA status, whereas within HR-positive disease, PIK3CA-mutated tumors showed only a modest trend toward lower pCR rates compared with wild-type, in the context of very small subgroup sizes.
Detailed genomic characterization of PIK3CA variants in the eight mutated patients is reported in Table 5. Hotspot mutations in exons 4, 9 and 20 were identified, along with a rare exon 7 variant, but the limited sample size did not allow robust correlation between specific variants and pCR.

3.3. Multivariable Analysis of pCR Predictors
Multivariable logistic regression analysis was performed to identify independent predictors of pCR among clinically relevant variables (Table 6).
In a model including HR status, tumor grade, and Ki-67 proliferation index (n = 56), HR status emerged as the only statistically significant independent predictor of pCR. HR-positive disease was associated with significantly lower odds of achieving pCR compared with HR-negative disease (OR 0.15, 95% CI 0.03–0.62; p = 0.009), confirming the univariate findings. Tumor grade (grade 3 vs. grade 2: OR 0.97, 95% CI 0.27–3.47; p = 0.958) and Ki-67 status (≥20% vs. <20%: OR 1.25, 95% CI 0.34–4.55; p = 0.734) were not independently associated with pCR in the multivariable model.
An exploratory multivariable analysis including PIK3CA mutational status was performed in the subset of 36 patients with available testing; however, this analysis was underpowered (only eight mutated cases) and yielded no statistically significant associations beyond a borderline trend for HR status (OR 0.14, 95% CI 0.02–1.05; p = 0.056). PIK3CA mutation status was not associated with pCR after adjustment for HR status and other covariates (OR 0.80, 95% CI 0.11–5.70; p = 0.824). These findings should be interpreted with caution due to the limited sample size and wide confidence intervals.

3.4. Secondary Endpoint: Early Survival Outcomes
At a median follow-up of 42 months (range 1.7–101.1), only five disease progression events and one death had occurred in the entire cohort. Given this low event rate, DFS and OS data are immature, median estimates are unreliable, and survival outcomes are summarized descriptively using landmark rates in Table 7, Table 8 and Table 9. No statistically robust differences by pCR, HR or PIK3CA status could be demonstrated, and all subgroup comparisons should be interpreted with caution as exploratory hypothesis-generating data.

3.5. Secondary Endpoint: Safety and Tolerability
All 56 patients were evaluable for safety. The THP regimen showed an excellent safety and tolerability profile, with AEs predominantly of grade 1–2 (Table 10).
Gastrointestinal (GI) toxicity was the most frequent class of event: diarrhea occurred in 62.5% of patients and nausea in 37.5%, with only 3.6% experiencing grade 3 diarrhea and no grade 3–4 nausea or vomiting.
Dermatologic and musculoskeletal events, including rash/dermatitis, onycholysis, myalgia and peripheral neuropathy, were generally mild (grade 1–2), and no grade 3–4 hematologic toxicity, febrile neutropenia, leucopenia, or thrombocytopenia was observed. Cardiac safety was excellent, with only one mild cardiac event and no grade 3–4 cardiac events, clinical heart failure, or treatment-related cardiac deaths. Importantly, no cases of clinically significant pulmonary toxicity, such as interstitial pneumonitis or drug-related pulmonary embolism, were reported despite the use of docetaxel. Overall, the favorable safety profile allowed completion of planned treatment in most patients.

4. Discussion
This observational analysis of 56 consecutive patients with HER2-positive EBC treated with neoadjuvant THP confirms the efficacy, safety, and clinical utility of dual HER2 blockade combined with taxane-based chemotherapy in this setting. The overall pCR rate of 60.7% observed in this cohort is consistent with major randomized trials and real-world evidence; in particular, the NeoSphere trial [4,5] showed that adding pertuzumab to trastuzumab plus docetaxel increased pCR rates from 29.0% to 45.8%.
Subsequent trials using dual HER2 blockade in combination with different taxane-based regimens (TRAIN-2 [7], TRYPHAENA [6], KRISTINE [8], NEOPETRA [9], GeparSepto [10]) have consistently reported pCR rates between 55% and 67%, and the 60.7% rate observed in our cohort lies well within this range. This concordance supports the standardization of the THP regimen as a neoadjuvant treatment option for HER2-positive EBC.
A key finding of this analysis is the identification of HR status as the main predictor of pCR, independent of other clinico-pathological variables. HR-negative patients achieved pCR in 85.7% of cases, compared with 45.7% in HR-positive patients (p = 0.007), corresponding to an approximately seven-fold higher likelihood of pCR (OR 7.125; 95% CI 1.87–27.15), and this 40-percentage-point absolute difference clearly exceeds what is typically reported for other molecular or clinical factors.
This observation is consistent with extensive evidence showing that HR-negative HER2-positive BCs are more sensitive to cytotoxic chemotherapy and anti-HER2 therapies. The underlying biological rationale relates to reduced “crosstalk” between HER2 signaling and the estrogen receptor (ER) pathway in HR-negative tumors: in the absence of an alternative HR-mediated proliferative drive, HER2-positive/HR-negative BCs are more dependent on HER2 signaling for growth and therefore more vulnerable to dual HER2 blockade [22].
Multivariable logistic regression analysis confirmed HR status as the only independent predictor of pCR in this cohort, with HR-positive disease associated with an approximately 85% reduction in the odds of achieving pCR (OR 0.15, 95% CI 0.03–0.62; p = 0.009) after adjustment for tumor grade and Ki-67 proliferation index. Neither grade nor Ki-67 retained independent prognostic significance in the multivariable model, suggesting that HR status is the dominant biological determinant of response to dual HER2 blockade in this setting. This finding aligns with extensive literature demonstrating that HR-negative/HER2-positive tumors exhibit markedly higher chemosensitivity and anti-HER2 therapy responsiveness compared with their HR-positive counterparts [23]. The biological mechanisms underlying the superior response to dual HER2 blockade in HR-negative versus HR-positive disease are multifactorial and involve complex crosstalk between HER2 and ER signaling pathways [24].
In HR-positive/HER2-positive tumors, ER activation provides an alternative proliferative drive that can partially compensate for HER2 inhibition, resulting in relative resistance to anti-HER2 therapy. Bidirectional interactions between ER and HER2 signaling—including ligand-independent ER activation via HER2-mediated phosphorylation and upregulation of HER family receptors in response to endocrine therapy—create escape mechanisms that reduce treatment efficacy [22].
Conversely, in HR-negative/HER2-positive tumors, cells are more dependent on HER2 signaling for growth and survival, rendering them particularly sensitive to dual HER2 blockade. The absence of ER-mediated resistance mechanisms, combined with higher proliferative activity (reflected by higher Ki-67 and grade 3 histology, as observed in our cohort), enhances chemosensitivity and contributes to the markedly higher pCR rates observed in this subgroup. Furthermore, HR-negative tumors may exhibit greater immune activation and enhanced antibody-dependent cellular cytotoxicity (ADCC) in response to trastuzumab and pertuzumab, thereby further augmenting treatment efficacy [25].
These findings underscore the importance of considering HR status not merely as a descriptive variable but as a key biological determinant that shapes therapeutic response and should inform treatment decision-making and future de-escalation strategies.
The clinical implications are substantial: HR status should be carefully considered when counseling patients regarding their likelihood of response and expected prognosis. The 85.7% pCR rate observed in HR-negative disease approaches the highest values reported in the literature and may support therapeutic de-escalation strategies tailored specifically to this favorable-prognosis subgroup [18,26].
In our cohort, PIK3CA mutations were detected in 22.2% of tested patients, in line with reported frequencies in HER2-positive BC, and pCR rates appeared similar in mutated and wild-type tumors. However, this exploratory analysis was constrained by the small number of mutated cases and the lack of pre-specified statistical power and therefore cannot exclude a clinically relevant impact of PIK3CA on treatment response. The observation that all HR-negative patients with PIK3CA-mutated tumors achieved pCR is intriguing and suggests that, under potent dual HER2 blockade, HR-negative disease may remain highly chemo-sensitive even in the presence of PI3K pathway alterations, but this hypothesis requires validation in larger, biologically annotated series.
This unexpected result, although limited by small sample size, raises the hypothesis that potent dual HER2 blockade might partially overcome PI3K pathway alterations in HR-negative disease through near-complete suppression of HER2 signaling. However, this observation is hypothesis-generating and requires prospective validation in larger, biologically annotated cohorts before drawing mechanistic conclusions. It is particularly noteworthy that HR-negative patients with PIK3CA-mutant tumors achieved a 100% pCR rate (3/3) compared with rates between 40% and 52.6% in HR-positive mutant cases, reinforcing the notion that HR status is a stronger determinant of response than PIK3CA mutational status. This pattern suggests that, in HR-negative disease treated with dual anti-HER2 blockade, PI3K pathway alterations may not provide meaningful escape routes, unlike in HR-positive tumors where HR signaling offers an alternative proliferative drive.
Overall, these data support the use of anthracycline-free THP as a highly active neoadjuvant option for HER2-positive EBC in daily practice, particularly in HR-negative patients, without suggesting any immediate need for PIK3CA-based treatment selection in this setting. Nevertheless, given the retrospective, single-center design, the limited sample size and the exploratory nature of the biomarker analyses, molecular profiling should currently be viewed as complementary to, rather than replacing, established clinical decision-making until prospective validation becomes available [20].
The THP regimen showed excellent tolerability, with most AEs being grade 1–2 and very few grade 3–4 events, a particularly relevant finding given the combined use of three active agents. GI toxicity was the most frequent class of AEs (diarrhea 62.5%, nausea 37.5%), as expected with taxanes and targeted therapies, but severe GI toxicity was rare, with only two cases of grade 3 diarrhea and no grade 3–4 nausea or vomiting; dermatologic and musculoskeletal events (myalgia 26.8%, peripheral neuropathy 17.9%) were mainly grade 1–2 and thus generally manageable, and the absence of grade 3–4 hematologic toxicity—including no febrile neutropenia, leucopenia or thrombocytopenia—suggests a substantial clinical advantage over anthracycline-containing regimens.
Cardiac safety was excellent, with only one mild cardiac event (grade 1–2), no grade 3–4 events, no clinical heart failure and no treatment-related cardiac deaths, in sharp contrast with anthracycline-based neoadjuvant regimens, which are associated with an estimated 5–10% risk of clinically relevant cardiac dysfunction; this cardiac profile supports omitting anthracyclines from neoadjuvant treatment for HER2-positive BC, in line with evidence from the TRAIN-2 [7] and TRYPHAENA [6] trials.
At a median follow-up of 42 months, the low number of events (5 DFS, 1 OS) reflects the favorable prognosis of this intensively treated cohort. Although survival data are immature and preclude definitive conclusions, the event rate was numerically lower in HR-negative patients and in those achieving pCR, consistent with the known prognostic value of these factors. Longer follow-up is needed to assess whether the high pCR rates observed translate into sustained DFS and OS benefits.
The trend toward longer survival in patients with PIK3CA-mutant tumors compared with wild-type, although not statistically significant due to the small sample size, supports continued monitoring and extended follow-up to better clarify any time-dependent impact of PIK3CA mutations on disease course. This single-center observational study, conducted in a relatively small cohort (n = 56), has inherent limitations: the design entails potential selection and data-collection bias, and although follow-up duration is adequate for safety assessment, it remains relatively short to precisely define long-term survival outcomes.
Survival endpoints were not part of the original analysis plan and, given the very low event rate, the DFS/OS results reported in Table 7, Table 8 and Table 9 are descriptive only and cannot be considered definitive.
This study has several limitations that warrant acknowledgment. The retrospective, single-center design and relatively small cohort size (n = 56) limit the generalizability of the findings and increase the risk of selection bias. The absence of a control arm with anthracycline-containing regimens precludes direct comparison of efficacy and safety outcomes between anthracycline-free and anthracycline-based approaches. PIK3CA testing was available in only 36 patients (64% of the cohort), and with only eight mutated cases, the analysis of PIK3CA associations with pCR was substantially underpowered, as acknowledged in the Methods. The multivariable logistic regression analysis, while informative, was constrained by the limited number of events (34 pCR) and could not accommodate a comprehensive set of prognostic covariates without risk of overfitting; therefore, some potentially relevant variables (e.g., tumor size, nodal burden, menopausal status) could not be fully evaluated. Early DFS and OS analyses were immature due to the low number of events (five progressions, one death) and relatively short median follow-up, precluding definitive prognostic conclusions. Finally, as a real-world observational study without pre-specified hypotheses or formal statistical power calculations, all findings—particularly those related to PIK3CA—should be considered exploratory and hypothesis-generating rather than definitive.
Future prospective, multi-center studies with larger cohorts and pre-specified statistical power are needed to confirm the independent prognostic role of HR status and to definitively assess the impact of PIK3CA mutations on response to anthracycline-free dual HER2 blockade regimens. Integration of comprehensive genomic profiling, including additional resistance mechanisms beyond PIK3CA (e.g., PTEN loss, ESR1 mutations), alongside functional imaging biomarkers (e.g., 18F-FDG PET) could further refine treatment selection and identify patients most likely to benefit from de-escalated or intensified strategies. Validation of these biomarkers in prospective trials with adaptive designs would represent a meaningful step toward precision medicine in HER2-positive EBC.

5. Conclusions
This observational analysis of neoadjuvant THP in 56 consecutive patients with HER2-positive EBC confirms the efficacy, safety, and clinical value of this therapeutic approach. These findings support the use of dual HER2 blockade with pertuzumab and trastuzumab combined with taxane-based neoadjuvant chemotherapy as a standard treatment.
In this real-world cohort, HR status, rather than PIK3CA mutational status, emerged as the main determinant of pCR under anthracycline-free THP, although the exploratory design and small biomarker-tested subset preclude definitive conclusions. While our findings do not indicate a clear negative effect of PIK3CA mutations on response, they should primarily be regarded as hypothesis-generating and as a rationale for future biomarker-driven de-escalation trials in HER2-positive EBC.
The excellent safety profile—especially the lack of clinically relevant hematological and cardiac toxicity—supports the omission of anthracyclines from neoadjuvant regimens in HER2-positive disease when dual anti-HER2 blockade is used, in line with recent de-escalation trial data.
Longer follow-up of this cohort will be essential to determine whether the high pCR rates, particularly in HR-negative patients, translate into sustained improvements in DFS and OS. It will also be important to explore additional molecular biomarkers of response and resistance beyond PIK3CA mutations to identify patients who may benefit most from treatment intensification or alternative therapeutic strategies; prospective studies incorporating real-time molecular profiling and adaptive trial designs could further optimize treatment selection and represent a step toward precision medicine in HER2-positive BC.