Uterine
leiomyosarcomas are rare malignant
tumors with a poor prognosis while
leiomyomas are common benign
tumors unrelated to their malignant counterparts. Diagnostic features commonly present in
leiomyosarcoma include cytologic atypia, high mitotic index, and a
sarcoma-specific geographic cell death designated '
tumor cell
necrosis (TCN)'. TCN has a sharp viable-nonviable boundary lacking
inflammation,
fibrosis or granulation tissue seen in nonspecific
infarction. These characteristics are sometimes difficult to interpret on routine
hematoxylin and
eosin slides, and can lead to diagnostic errors. In this study, we used extracellular matrix stains to test the hypothesis that the host response which characterizes nonspecific
infarction may degrade the matrix in infarcted
tumor more than in TCN. A 'honeycomb' pattern of
reticulin highlighted individual
tumor cells in viable regions of all cases. Nonviable area of
reticulin patterns differed significantly by diagnosis (P<0.001), with a honeycomb pattern maintained (91%, 20/22) in
leiomyosarcoma and lost (61%, 11/18) in
leiomyomas. Retention of honeycomb
reticulin in nonviable areas of
leiomyosarcoma occurred irrespective of the presence of
inflammation,
hemorrhage,
fibrosis, or diffuse hyalinization.
Fibrosis/hyalinization as evidenced by
trichrome stain was significantly (P<0.001) more common in nonviable areas of benign
leiomyomas (100%, 18/18) compared with
leiomyosarcomas (36%, 8/22). In those occasions where viable tissues contained discernable polarization of mitotic activity, these decreased toward the nonviable interface in
leiomyosarcoma, and had an opposite pattern in
leiomyomas, increasing toward the interface. There is a significant difference in the
reticulin and
collagen networks of nonviable areas of
leiomyosarcoma compared with
leiomyoma. At the time of early injury, both retain
reticulin; however, this is cleared over time in benign, but not malignant, areas of
necrosis. We conclude that proliferative repair of
leiomyomas at the viable-nonviable interface includes remodeling of the extracellular matrix, in contrast to the static preservation of extracellular matrix ('mummification') in nonviable areas of
leiomyosarcomas.