In search of zebras: Critical analysis of the rarity of perineural breast cancer spread to the brachial plexus in men

Abstract

BackgroundPerineural spread (PNS) of breast cancer to the brachial plexus is rare with reports limited to cases only in female patients. The purpose of this study was to determine the incidence of PNS in male as compared to female patients. MethodsAdult breast cancer patients referred to a single institution between 1994 – 2022 were retrospectively reviewed for imaging or biopsy confirmed cases of PNS to the brachial plexus. A systematic review of the literature was performed by two independent reviewers for articles published in any language between 1990 – 2022 in PubMed, Scopus, Embase, and Google Scholar. ResultsOf the 10,466 patients with breast cancer (10,355 female, 111 male) referred to a single institution, there were 42 female patients with PNS to the brachial plexus for an estimated incidence of 0.4%. In the same time period, there were 111 male patients treated for breast cancer, including 88 patients with Klinefelter’s syndrome (KS); however, there were no cases of male patients with PNS. A systematic review of the world’s literature also did not identify any male patients with PNS to the brachial plexus. ConclusionsThere is a lack of any reported cases of PNS of breast cancer to the brachial plexus in men or patients with KS, who have a much higher incidence of breast cancer. This may reflect either the compounding rarity of these two events or point towards a distinct hormonally-driven link between breast cancer and PNS, highlighted by the disparity in PNS incidence in men and women.