Immunohistochemical methods were used to demonstrate the distribution of basement membrane
laminin and
type IV collagen in eight
tumors derived from striated muscle (three botryoid, two alveolar, and two adult-type
rhabdomyosarcomas; one benign vaginal
rhabdomyoma). All of the
tumors produced significant amounts of both basement membrane components. Stainings clearly revealed the alveolar nature of the
rhabdomyosarcomas, with the alveolar spaces surrounded by distinct basement membranes. Different stages of cellular development were identified in the botryoid
sarcomas, with the most immature cells of the cambium layer devoid of external basement membrane around the
tumor cells, although the stroma contained finely dispersed basement membrane material and some cells contained intracytoplasmic
laminin or
type IV collagen, indicative of the synthesis of these
proteins. The more mature cells, which had abundant granular cytoplasm, were enveloped by distinct basement membranes and seemed to have coalesced, forming structures resembling myotubes. The adult-type
rhabdomyosarcomas were composed of large pleomorphic cells that were surrounded by basement membranes, either individually or in small groups. Some giant cells contained intracytoplasmic
laminin. The vaginal
rhabdomyoma was composed of round rhabdoblastic cells or elongated strap cells with cross-striations. Cells of both of these types were surrounded by thin but distinct basement membranes. The results suggest that demonstration of basement membranes would be helpful in the diagnosis of
tumors derived from striated muscle. The findings concerning different stages of maturation of
tumor cells are in accordance with previous in vitro observations of myoblastic cells.