NF-1, or von Recklinghausen's disease, was first described in 1882. It is a relatively common autosomal hereditary dominant disorder that equally involves men and woman and has variable expression, a frequency of one per 3000 births, and a high rate of new mutations [
4]. The genetic basis of the disease is a mutation located on chromosome 17q11.2 [
1]. NF-1 is characterized by brown skin pigmentation ('café au lait' spots), cutaneous neurofibromas and neoplasms of the peripheral or central nervous system. The association between NF-1 and tumors of neurogenic and neuroendocrine origin, such as meningiomas, gliomas and pheochromocytomas, is well known. Malignancies are found in 3% to 5% of patients. GI involvement is present in approximately a quarter of cases [
2]. GI involvement in NF-1 commonly occurs in four principal forms: hyperplasia of the gut neural tissue, multiple GI stromal tumors (GISTs), duodenal or periampullary endocrine tumors and a miscellaneous group of other tumors. GISTs are the most common of these forms [
1]. Although there have been scattered reports of adenocarcinoma of the GI tract complicating peripheral neurofibromatosis [
1,
3], few cases have explored the association of primary infiltrating adenocarcinoma of the stomach [
5]. It has been indicated that loss of function of the
NF-1 gene results in peripheral neurofibromatosis [
6], but no definite reasons have been cited for the high incidence of primary malignant tumors in these patients. The
NF-1 gene and the
p53 tumor suppressor gene are both located on chromosome 17 (6), suggesting that the
p53 gene is mutated in several NF-1-associated tumors [
7]. Researchers have sought to determine the role of
p53 tumor suppressor genes in the etiopathogenesis of NF-1-associated malignant primary tumors. In a recent study, a germline
NF-1 nonsense mutation in exon 37 was detected by DNA sequence analysis, showing that the GI tumor arose through
NF-1 gene inactivation [
8]. The
NF-1 gene product, neurofibromin, contains a guanosine 5'-triphosphate (GPT)ase-activating protein-related domain that is able to down-regulate p21ras by stimulating its intrinsic GPTase. Because p21ras-GPT is a major regulator of growth and differentiation, mutant neurofibromins resulting from somatic mutations in the
NF-1 gene might interfere with ras signaling pathways and contribute to the development of tumors [
9]. These results suggest a causal association between NF-1 and the development of gastric cancer in our case.
AFP- positive cases have been found among disorders other than hepatocellular carcinoma, such as hepatitis, liver cirrhosis and metastatic cancer of the liver. Additionally, elevated levels of serum AFP have been reported to occur with several tumor types other than hepatocellular carcinoma and embryonic cell carcinoma [
10]. These elevated levels have largely been associated with neoplasms of the GI tract [
11]. In the GI tract, an elevation of the serum AFP level was reported in 1.3% to 15% of gastric cancers [
10]. The authors described AFP-producing gastric adenocarcinomas with a high serum AFP level and synchronous hepatic metastasis. Gastric cancers that secrete AFP are rare. The first case was described in 1970 [
11]. AFP-secreting gastric cancers occur with a frequency of 2% to 6%. The prognosis of these cases tends to be poor with a high frequency of hepatic metastasis at presentation. Liver metastasis has been reported to occur in 70% to 80% of cases. Our patient had an elevated serum AFP level and a gastric cancer with liver metastasis without viral hepatitis or liver cirrhosis; however, the immunohistochemical analysis showed that the tumor was AFP-negative. Previous authors reported the occurrence of gastric adenocarcinoma with a high serum AFP level and synchronous hepatic metastasis [
12]. It has subsequently become clear that there are two distinct histologic subtypes: a medullary type and a papillary or tubular type. The medullary type tends to stain more strongly for AFP [
12]. Our case showed moderately differentiated tubular adenocarcinoma. Additionally, an immunohistochemical analysis showed that the cells present in the metastatic liver tumor and the gastric lesion were AFP-negative. The regulation of gastric cancer cell lines by hepatocyte growth factor (HGF) and
c-metproto- oncogene
(c-Met) has been described recently [
13]. HGF is strongly associated with the progression of cancer cells to invasive phenotypes and the development of distant metastases. A higher incidence of
c-Met overexpression was found in AFP-secreting tumors, as well as a higher expression in poorly differentiated tumors in the AFP-positive group than in those that were AFP-negative [
13]. A serum AFP level over 500 ng/mL in gastric cancer is rare.
Studies have correlated levels of CA 72-4 with findings of pathologic examinations in gastric carcinoma. These have shown significantly higher marker levels associated with gastric serosa invasion by the neoplasia and invasion of veins or lymphatic vessels into the gastric wall as well as lymph-nodal metastases [
14]. A more advanced stage of gastric cancer (stage III and IV) results in higher serum levels of CA 72-4. Our patient had a normal CA 19-9 serum level. Elevated serum levels of CA 19-9 have been described in 25% to 48% of patients with gastric cancers, but these patients had multiple liver metastases. No correlation was found between serum CA 19-9 level and the stage of gastric cancer [
15].