Selective location of palisaded myofibroblastoma with amianthoid fibres.

The occurrence of a palisaded myofibroblastoma with amianthoid fibres in the left inguinal lymph node of a 51 year old man prompted an investigation of the factors underlying its exclusive location. The antigen profile was characterised which confirmed the homogeneous expression of vimentin and smooth muscle actin as well as the lack of desmin. Use of monoclonal antibodies to check for a differential distribution of myofibroblasts and the putative cell of origin of palisaded myofibroblastoma showed that inguinal lymph nodes have abundant vimentin and actin positive cells and desmin negative cells. This suggests that the selective occurrence of myofibroblastoma is related to the nodal microenvironment, providing a source of available and potentially proliferating myofibroblasts. Mast cells abounded in this lesion, particularly around amianthoid fibres, as well as in pelvic and inguinal lymph nodes. In view of the known role of mast cells in interstitial matrix degradation it is postulated that the core of amianthoid fibres represents degraded interstitial matrix, analogous to the sclerotic areas commonly found in the above mentioned lymph node groups, while the peripheral spokes, so peculiar to this entity, are the result of vimentin and smooth muscle actin, directly shed by proliferating myofibroblasts.