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Many individuals undergoing treatment for early-stage breast cancer frequently face difficulties in consistently adhering to their prescribed long-term hormone therapy following lumpectomy, according to a comprehensive analysis of U.S. insurance claims. This research offers valuable insights into real-world treatment adherence, particularly concerning strategies that involve forgoing radiation therapy, which often assume steadfast patient compliance with medication regimens for at least half a decade.

The study indicated that fewer than one-third of patients managed to maintain adherence above a recognized threshold throughout the entire five-year endocrine therapy period. Notably, individuals who did not undergo radiation therapy were found to have a higher propensity for significant gaps in medication adherence compared to those who did. Furthermore, younger patient age was identified as a factor linked to reduced adherence levels. These findings were unveiled at the American Society for Radiation Oncology (ASTRO) Annual Meeting.

Dr. Shannon Jiang, the lead author of the study and a radiation oncology resident physician at Washington University School of Medicine in St. Louis, emphasized the critical implications of these findings. "While radiation therapy post-lumpectomy is a proven method for preventing local breast cancer recurrence, its omission in certain low-risk cases relies heavily on consistent long-term endocrine therapy. Our data suggest that sustaining a daily medication for five years presents a considerable challenge in everyday clinical practice, often more so than commonly anticipated."

Typically, after a lumpectomy for hormone receptor-positive early-stage breast cancer, patients receive radiation therapy to minimize the risk of recurrence in the treated breast, alongside endocrine therapy to mitigate the overall risk of cancer return. For specific older patients with low-risk disease, clinical trials have shown that radiation therapy can be safely omitted without affecting overall survival, though it may increase local recurrence risk. In these trials, endocrine therapy was an integral part of the treatment plan, making long-term medication a cornerstone of the radiation-sparing approach.

Endocrine therapy works by inhibiting or reducing the hormones that fuel hormone receptor-positive breast cancer. However, this treatment often comes with side effects such as hot flashes, fatigue, joint discomfort, bone health concerns, and cognitive changes, which can make consistent adherence over several years challenging for patients.

Dr. Jiang further elaborated, saying, "Our study serves as a crucial reminder that the doctor's prescription for five years of endocrine therapy and the patient's actual completion of those five years are not necessarily equivalent. When radiation therapy is excluded from the treatment protocol, endocrine therapy gains even greater importance in preventing cancer recurrence. It is imperative that we engage in candid discussions with patients considering this approach, outlining the demands of long-term treatment and its potential impact on their quality of life."

The research team analyzed data from 17,025 patients aged 23 to 64 with hormone receptor-positive, early-stage breast cancer, drawn from Merative MarketScan commercial and multistate Medicaid claims. All participants had undergone lumpectomy and filled at least one endocrine therapy prescription, with 89% also receiving radiation therapy.

The researchers utilized pharmacy claims to assess patients' medication possession ratio, a metric that indicates the consistency with which prescriptions were filled. While this measure doesn't confirm daily pill intake, it provides a proxy for whether patients had sufficient medication available to follow their prescribed regimen.

According to the standard definition, patients were classified as adherent if they had medication available for at least 80% of the observation period. The study also explored less stringent thresholds of 70%, 60%, and 50% possession to identify progressively larger gaps in medication availability.

The overall findings revealed that approximately 28% of patients consistently adhered to the 80% threshold throughout the five-year follow-up period. Although annual adherence rates appeared higher, ranging from 59% to 75% in individual years, the longitudinal analysis clearly demonstrated a gradual decline in the number of patients maintaining adherence over time.

The omission of radiation therapy was linked to a greater risk of nonadherence to long-term endocrine therapy. Patients who did not receive radiation therapy were twice as likely to drop below the 50% medication-possession threshold over time and showed significantly higher probabilities of falling below the 60% and 70% benchmarks. The statistical significance for this association was not observed at the standard 80% adherence threshold.

It is important to note that the study's design did not aim to establish a causal link between receiving radiation therapy and improved adherence. The observed differences could stem from variations in healthcare access or treatment preferences among patient groups, or from the more frequent contact with oncology teams during radiation treatment. Younger age was also found to be a predictor of nonadherence, with patients under 60 exhibiting a 20% to 25% higher risk of becoming nonadherent across all studied thresholds. Dr. Jiang highlighted the increasing relevance of this finding as more research focuses on radiation therapy omission in younger patients with favorable tumor characteristics.

Given that the database excluded patients over 64, the study could not determine if adherence patterns differ in older populations, which currently constitute a significant portion of those considered for radiation therapy omission. Dr. Jiang mentioned that the team plans to integrate Medicare data to investigate adherence within this demographic. "Our primary objective is to equip clinicians with more accurate real-world data for patient counseling. The evidence guiding de-escalation strategies must be evaluated in conjunction with the long-term experiences of patients following treatment."

Dr. Jose G. Bazan, Chair of the ASTRO Breast Cancer Resource Panel and a radiation oncologist at City of Hope Comprehensive Cancer Center in Duarte, California, provided an expert perspective. "Omitting radiation therapy can be a suitable option for carefully selected individuals with lower-risk breast cancer, but endocrine therapy remains a crucial component of such a strategy. This study enriches treatment discussions by illustrating the inherent challenges of long-term adherence. When considering radiation omission, clinicians should weigh the established benefits of local control from radiation against the practical difficulties patients face in maintaining endocrine therapy for extended periods. The ultimate goal is to select a treatment plan that patients can realistically sustain over time."