Abstract ES4-3: What is the value of internal mammary chain RT and how can we deliver it safely?
Authors: Yarnold John R 
Published: May 2015

The 2014 systematic overview of post-mastectomy radiotherapy (RT) in pN+ patients randomized ± local-regional RT reported absolute 7.9% (SE 3.1) and 9.3% (SE 2.7) reductions in 20-year breast cancer mortality in women with 1-3 and 4+ positive nodes, respectively [1]. Most patients were given RT to axilla, supraclavicular fossa (SC) and internal mammary chain (IM); hence, it is impossible to calculate what IM-RT contributes.

Three randomised trials (French n=1334; MA.20 n=1832; EORTC n=4004) have specifically tested IM-RT, 2 of which included medial SC in the randomisation. All patients received axillary dissection (AD) and mastectomy/tumour excision, with an average 62% axillary node positivity. Table 1 lists the treatments delivered.

Table 1TreatmentFrenchMA.20EORTCSurgeryMastectomy + ADMastectomy/Breast conservation + ADMastectomy/Breast conservation + ADRT ControlChest wall + axillary apex + medial SCChest wall or breastChest wall or breastRT Test (in addition to Control)IMIM + medial SCIM + edial SC

No trial detected a statistically significant benefit in overall survival (OS), but early metanalysis of the 3 studies suggests a statistically significant improvement in OS (HR 0.88 95% CI 0.80-0.97) in patients allocated IM-RT with/without additional SC-RT [2]. Disease-free (DFS), metastasis-free (MFS) and overall survival (OS) benefits are shown in Table 2.

Table 2ResultsFrenchMA.20EORTCDFSAbsolute 3.3% gain (10yr, NS)HR 0.67 (95% CI 0.52-0.87)HR 0.89 (95% CI 0.80-1.00)MFS-HR 0.64 (95% CI 0.47-0.85)HR 0.86 (95% CI 0.76-0.98)OSAbsolute 3.3% gain (10yr, NS)HR 0.76 (95% CI 0.56-1.05) Absolute 1.6% gain (5yr, NS)HR 0.87 (95% CI 0.76-1.0) Absolute 1.6% gain (10yr, NS)

The sole trial (French) to report arm swelling recorded a small (3.1%) absolute excess of grade 2 arm lymphedema after IM-RT; the other 2 trials reported no excess cardiac toxicity. Only the French trial is published as a full manuscript, and until this is the case for the other 2 trials, it is impossible to say how specific and robust guidelines will be. Assuming the benefits of IM-RT rely on eradication of IM metastases, factors associated with risk of IM involvement include macroscopic involvement of multiple axillary nodes and central/medial quadrant tumours. Recommendations based on sentinel IM node biopsy, lymphoscintigraphy or positron emission tomography are likely to be may be desirable. Accurate mediastinal staging may not resolve all issues, as the current debate challenging the need to treat the axilla in women with axillary micrometastases illustrates.

The 2 commonly-used techniques involve simple 3D forward planned dosimetry that is usually able to satisfy standard constraints for organs at risk. The IM is encompassed within wide tangential beams in 1 technique, and as an extension of an anterior SC beam in the other. Example of each will be presented.

1. EBCTCG. Effect of radiotherapy after mastectomy and axillary surgery on 10-year recurrence and 20-year breast cancer mortality: Meta-analysis of individual patient data for 8135 women in 22 randomised trials. Lancet, 2014. 383: p. 2127-25.

2. Budach, W., et al., Adjuvant radiotherapy of regional lymph nodes in breast cancer - a meta-analysis of randomized trials. Radiat Oncol, 2013. 8: p. 267.

Citation Format: John R Yarnold. What is the value of internal mammary chain RT and how can we deliver it safely? [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr ES4-3.