Ten Percent Plexopathy Is Acceptable in This Case

Metastatic infiltration of breast cancer into the brachial plexus (BP) is rare. Symptoms can occur years after initial diagnosis and can be confused with treatment-related complications. Diagnostic workup can include electromyography, BP magnetic resonance imaging (MRI), positron emission tomography with computed tomography and/or nerve biopsy to ensure accurate diagnosis. The gold standard in this setting is MRI, with a sensitivity of 95% for detecting perineural invasion and 63% for mapping the entire extent of perineural spread.1Nemzek WR Hecht S Gandour-Edwards R et al.Perineural spread of head and neck tumors: How accurate is MR imaging?.AJNR Am J Neuroradiol. 1998; 19: 701-706PubMed Google Scholar The clinical target volume of involved nerves can be extended proximally to their site of origin—in this case, at the spinal cord levels C5 to T1. At the time of initial BP involvement, 40 Gy in 15 fractions (equivalent dose in 2-Gy fractions (EQD23) of 45.3 Gy) followed by a boost of 10 Gy in 5 fractions (EQD23 of 10 Gy) was delivered. Assuming an α/β ratio of 3, an initial, more fractionated regimen such as 60 Gy in 30 fractions may have allowed for dose escalation with minimally increased risk of toxicity.2Yan M Kong W Kerr A et al.The radiation dose tolerance of the brachial plexus: A systematic review and meta-analysis.Clin Transl Radiat Oncol. 2019; 18: 23-31Abstract Full Text Full Text PDF PubMed Scopus (23) Google Scholar Of note, estimates of the α/β ratio of breast cancer range from 2.2 Gy to 10.0 Gy.3van Leeuwen CM Oei AL Crezee J et al.The alfa and beta of tumours: A review of parameters of the linear-quadratic model, derived from clinical radiotherapy studies.Radiat Oncol. 2018; 13: 96Crossref PubMed Scopus (269) Google Scholar At time of recurrence, if accepting a 10% chance of BP injury, a total EQD23 of 90 Gy could be delivered to the BP.4Morse RT Doke K Ganju RG et al.Stereotactic body radiation therapy for apical lung tumors: Dosimetric analysis of the brachial plexus and preliminary clinical outcomes.Pract Radiat Oncol. 2022; 12: e183-e192Abstract Full Text Full Text PDF PubMed Scopus (6) Google Scholar This would leave an EQD23 of 35 Gy that could be prescribed to the BP this time. This could be delivered as 34 Gy in 15 fractions to the BP with a simultaneous integrated boost of 40 Gy in 15 fractions to the nonoverlapping area of spinal cord. Admittedly, the use of the linear quadratic equation to estimate cumulative toxicity risk is imperfect, but given the inevitable plexopathy that may arise without further radiation therapy, this dose and fractionation with a relatively low risk of radiation-induced toxicity warrants consideration. In summary, it is our opinion that the authors5Anakwenze Akinfenwa CP Strom EA A case of metastatic breast cancer to the brachial plexus with direct infiltration of the intramedullary cervical and thoracic spinal cord.Int J Radiat Oncol Biol Phys. 2022; 114: 181-182Abstract Full Text Full Text PDF PubMed Scopus (3) Google Scholar used an appropriate dose of radiation up front that straddled palliative and curative-intent regimens in terms of its overall risk and efficacy, which appears appropriate for this patient with apparent oligoprogression. In hindsight given the recurrence, an initial aggressive, conventionally fractionated regimen encompassing a larger portion of the BP may have optimized outcomes, although with a slightly higher risk of radiation-induced plexopathy. From the Plexus to the Cord: A Case of Metastatic Breast CancerInternational Journal of Radiation Oncology, Biology, PhysicsVol. 114Issue 2PreviewIn 1998, a 46-year-old professional model presented with breast cancer with axillary, infraclavicular, liver, and lung metastasis. She completely responded to systemic therapy but developed brain metastasis treated in 1999 with resection and scalp-sparing whole brain radiation. She continued modeling and remained with no evidence of disease before recurring locally and undergoing lumpectomy and radiation in 2002. After a breast and infraclavicular recurrence, she received chemotherapy followed by modified radical mastectomy in 2005. Full-Text PDF