PracticeUpdate: Haematology & Oncology

CONFERENCE COVERAGE

8

58th annual meeting of the American Society for Radiation Oncology (ASTRO)

25–28 SEPTEMBER • BOSTON, UNITED STATES

With 11,000 attendees from the radiology community, the 2016 ASTRO annual meeting showcased the latest in radiation therapy techniques and technologies. The PracticeUpdate Editorial Team reports from Boston on some of the highlighted clinical trial data presented at the meeting.

A radiation boost is recommended in patients with DCIS and ≥10 years life expectancy following breast-conserving surgery and whole breast radiotherapy A supplemental boost of radiation has been shown to improve local control and provide an incremen- tal benefit in decreasing breast cancer recurrence for patients with ductal carcinoma in situ (DCIS) who receive whole breast radiation therapy fol- lowing lumpectomy. This finding of a retrospective analysis was reported at the ASTRO 2016. M eena Savur Moran, MD, of Yale School of Medicine, NewHaven, Connecticut, explained that patients with DCIS undergoing breast conservation therapy typically receive a lumpectomy, followed by whole breast radiotherapy. Many then receive an additional boost of radiation of four to eight fractions to the surgical bed. While multiple clinical trials have demonstrated a modest but statistically significant reduction in ipsilateral breast tumour re- currence from a radiation boost after whole breast radiotherapy for invasive breast cancer, no phase 3 studies have evaluated radiation boost for DCIS. Ten academic institutions from the US, Canada, and France provided de-identified data for 4131 cases of DCIS, the largest cohort of patients with DCIS treated with or without boost to date. Eligible patients included those with pure DCIS (ie, no microinvasion) who received whole breast radiotherapy with or without radiation boost and reached at 5 years of follow-up. They received either electron or photo radiation boost. The

The benefit in reducing in-breast recurrence was demon- strated across all age subgroups. Furthermore, treatment with the DCIS boost was an independent predictor of decreasing ipsilateral breast tumour recurrence on multivariate analyses that controlled for grade, necrosis, margin status, age, tumour size, and tamoxifen use. On subset analysis, though the boost did not convey a statisti- cally significant benefit in the subset of patients with positive margins, it did independently predict for reducing ipsilateral breast tumour recurrence in all age groups with negative mar- gins (all P < 0.02). Dr Moran explained that only 4% of partici- pants comprised the subset of patients with positive margins. It is highly likely, therefore, that the positive margin subset was underpowered to show a statistically significant benefit. Dr Moran stated, “Our findings suggest that adding several additional fractions of radiation directed to the lumpectomy cavity after whole breast radiation for DCIS provides an incre- mental benefit in decreasing local relapse, similar in magni- tude to the benefit of 4% at 20 years of the boost for invasive cancers.” “While these small numbers may not seem substantial, the boost data in invasive disease have highlighted the clinical importance that small decreases in local relapse provide for patients. Ultimately, these small decreases in ipsilateral breast tumour recurrence reduced the number of mastectomies for recurrence by approximately 40% in patients who had received a boost vs those who did not.”

median boost dose was 14 Gy. Records documenting patients receiving a brachytherapy boost, those with unknown boost status, and those who receive partial breast radiation were not included in the analysis. Among 4131 cases included in the analysis, 2661 patients received a radiation boost and 1470 did not. Radiation boosts were more common for patients with positive margins follow- ing breast-conserving surgery, those with unknown oestrogen receptor status, and individuals with documented necrosis. Median follow-up was 9 years. Patients with DCIS who received a radiation boost following whole breast radiotherapy experienced a reduction in local recurrence. Ipsilateral breast tumour-free survival for boost versus no boost, was 97.1 versus 96.3% at 5 years, 94.1 versus 92.5% at 10 years, and 91.6 versus 88.0% at 15 years following treatment, respectively (P = 0.013). Dr Moran remarked, “Many radiation oncologists routinely deliver a boost after whole breast radiotherapy for DCIS. We anticipated a similar benefit to that of invasive cancers. But we haven’t had consistent data to demonstrate this benefit in DCIS.” She continued, “Our study has demonstrated that a radiation boost provides an albeit small but significant long-term benefit in reducing breast tumour recurrence for patients with DCIS. The results support consideration of a boost in patients with DCIS who undergo whole breast radiotherapy and have life expectancies of 10 or more years.”

PRACTICEUPDATE HAEMATOLOGY & ONCOLOGY