Perineural "Invasion"

A 46 year old woman underwent ultrasound guided core biopsy because of a breast mass.

Image 1.  Two lobular units, one of which has focal apocrine cytology.

Image 3.  Immunohistochemistry using antibodies to p63 highlight myoepithelial cells in normal acini and within the perineural glands.

Image 2.  Small apocrine glands are intimately associated with a nerve, adjacent to a lobular unit.

Image 4.  Higher power of image 3.

Image 5.  Immunohistochemistry using antibodies to smooth muscle myosin heavy chain, demonstrating basement membrane material in normal acini and in perineurial glands.

Diagnosis:  Benign perineurial adenosis

Discussion:  The mass in this case was a radial scar (not shown), and also areas of adenosis, including adenosis in a perineural location.  

In some organs, the presence of glands in a perineural location is evidence of neoplasia, but as this case illustrates, perineural glands may be seen in benign conditions of the breast.  The presence of glands next to a nerve is a purely incidental finding.  The reference given below describes this phenomenon, however using the term ‘invasion’ for a benign condition can be misleading and should be avoided.   

Reference:  Taylor HB, Norris HJ.
Epithelial invasion of nerves in benign diseases of the breast. Cancer 1967; 20:2245-9.