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

BACKGROUND

Perineural spread (PNS) of breast cancer to the brachial plexus is rare, with reports limited to cases only in female patients. This study aimed to determine the incidence of PNS in male compared with female patients.

METHODS

Adult breast cancer patients referred to a single institution between 1994 and 2022 were retrospectively reviewed for imaging or biopsy-confirmed cases of PNS to the brachial plexus. Two independent reviewers of articles published in any language between 1990 and 2022 in PubMed, Scopus, Embase, and Google Scholar performed a systematic literature review.

RESULTS

Of 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 did not identify male patients with PNS to the brachial plexus.

CONCLUSIONS

There 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 toward a distinct hormonally-driven link between breast cancer and PNS, highlighted by the disparity in PNS incidence in men and women.