The treatment strategy for mesenchymal
tumors of the gastrointestinal tract is based upon typing of the
tumor. Especially differential diagnosis of
gastrointestinal stromal tumors (GISTs) to
leiomyomas is crucial for determining radicality of surgery.
L1 cell adhesion molecule (CD171) plays an essential role in
tumor progression. The aim of this study was to determine expression of L1 in GISTs,
smooth muscle tumors,
desmoid-type
fibromatosis and
peripheral nerve sheath tumors (PNSTs). We retrospectively analyzed a total of 129 surgically resected primary
tumors or
metastases of 72 GISTs, 29
smooth muscle tumors, seven PNSTs and 21
desmoid-type
fibromatosis by immunohistochemistry for c-kit, CD34, smooth muscle actin,
desmin,
vimentin, S-100 and L1 expression. L1 expression was detected in 53 (74%) of 72 GISTs but in none of 29
smooth muscle tumors or 21
desmoid-type
fibromatosis (P<0.01 by Fisher's test). In all, four (57%) of seven
peripheral nerve sheath tumors were L1-positive. Survival analysis of 55 surgically completely resected GISTs presenting without
metastasis at initial diagnosis revealed no
tumor-specific death among L1-negative patients (P=0.13 by log-rank test; median follow-up time 41 months) and one recurrence was observed (P=0.12). Interestingly high levels of L1 were seen in
tumor vascular endothelial cells of
smooth muscle tumors and PNSTs, but not in GISTs. Our data show that L1 is highly expressed in GISTs but not in
smooth muscle tumors and
desmoid-type
fibromatosis being important differential diagnoses. The trend towards a reduced survival of L1-positive patients in this study has to be further evaluated in future trials with higher patient numbers.