These data suggest that elevation of p21ras may be a common event in early stages of colon tumors, and tumor progression may lead to a more autonomous population of cells in which other growth factors supplant the role of this protein.
Further analysis of the chromosome breaks in this group of lymphomas suggested that those involving the SKI site probably are of importance in tumor progression.
The rearrangement of c-raf-1 may have occurred during transfection or may have been present in a small population of the original tumor cells as a result of tumor progression.
This small but extensively studied group of cases has indicated that increased c-erbB-2 protein can be identified routinely in fixed tissue sections, making it possible to carry out extensive studies to look for clinical correlates, but also to assess the stage in tumour progression at which the increased expression occurs and whether it correlates with any potentially premalignant condition.
The rearrangement of c-raf-1 may have occurred during transfection or may have been present in a small population of the original tumor cells as a result of tumor progression.
Expression of v-Ha-ras in biochemical variant SCLC cells directly demonstrates that important transitions can occur between phenotypes of human lung cancer cells and that these may play a critical role in tumor progression events in patients.
This finding implies independent amplification events and supports the idea that the amplification of myc genes is probably a secondary event correlated with tumor progression.
Each example of an activated ras gene showed a mutation at the 61st codon of the protein, with the exception of one melanoma which showed a mutation at codon 13 of the N-ras gene; (2) all the melanomas displaying an activated ras gene had a similar cell surface phenotype and appear to come from a similar phase of differentiation; (3) 5-6% of noncultured primary and metastatic melanomas have mutated ras genes; (4) no ras gene mutations were found in any precursor lesion, specifically normal nevi and dysplastic nevi; (5) immunoperoxidase analysis of paraffin-embedded specimens indicated no quantitative or qualitative alterations in p21 expression that correlate with tumor progression; (6) there were no observable differences in p21 expression between melanoma cells growing exponentially or in plateau phase, or between melanoma cells with or without ras mutations; nor were any cell kinetic differences found between cells with and without mutated ras genes.
MUC18, a marker of tumor progression in human melanoma, shows sequence similarity to the neural cell adhesion molecules of the immunoglobulin superfamily.
Because a loss of tumor cell HLA-A,B,C antigen or lymphocyte function-associated antigen 3 could be selected for through an advantage in escape from cytotoxic T-lymphocyte attack, our results suggest that immunoselection may be a more important mechanism in tumor progression than has previously been assumed.
Increased expression of this putative growth factor receptor has been reported to occur by molecular mechanism other than gene amplification and for this reason we have studied the expression of the p185 protein in normal colon and in lesions representing different stages of neoplastic progression.
Because a loss of tumor cell HLA-A,B,C antigen or lymphocyte function-associated antigen 3 could be selected for through an advantage in escape from cytotoxic T-lymphocyte attack, our results suggest that immunoselection may be a more important mechanism in tumor progression than has previously been assumed.
One patient with follicular small cleaved cell NHL that evolved to a small noncleaved cell NHL had coexisting bcl-2 and c-myc rearrangement in the aspiration specimen of the high-grade NHL, suggesting sequential bcl-2 and c-myc activation during the tumor's progression.
This in vivo rearrangement of the c-myc gene specific to tumor cells may represent one mechanism of activation of a protooncogene during tumorigenesis or tumor progression in human cancer.
In contrast, MGSA mRNA was constitutively expressed in the absence of exogenous growth factors in cultures established from benign intradermal and dysplastic nevi and melanoma lesions in different stages of tumor progression.