Field guide to local flaps.

Local skin flaps are an integral part of the dermatologic surgeon's reconstruction efforts. An understanding of the basic categories of flaps and their characteristics is essential. This article reviews the broad categories of flaps and common examples of each.

Harvey ras (H-ras) point mutations are induced by 4-nitroquinoline-1-oxide in murine oral squamous epithelia, while squamous cell carcinomas and loss of heterozygosity occur without additional exposure.

Tumorigenesis is a multistep genetic process requiring several somatic mutations for neoplastic transformation. These mutations appear to be sequential, random, and independent events. However, we find linked, nonrandom ras mutations occurring during 4-nitroquinoline-1-oxide-induced tumorigenesis months after exposure to the carcinogen had ceased. The carcinogen had been topically applied to the oral cavity of CBA mice for 4 to 16 weeks. Dysplasia developed after 24 weeks, and carcinoma in situ and squamous cell carcinoma developed after 28 weeks. H-ras mutations were detected in 13 of 25 tissue specimens (10 of 14 invasive carcinomas and 2 of 4 carcinoma in situ, 1 of 5 dysplastic tissue, and 0 of 2 normal tissues). Approximately one-half of the tumors had G to A point mutations at codon 12 of the cellular H-ras proto-oncogene on mouse chromosome 7. None had codon 11, 13, or 61 mutations. Loss of heterozygosity occurred in 5 of 14 invasive cancers. Larger invasive squamous cell carcinomas consistently lost the wild-type allele, whereas preneoplastic lesions and small tumors were heterozygous for ras. This suggests a causal relationship between carcinogen treatment, H-ras activation, and initiation of tumorigenesis. The wild-type allele in mouse chromosome 7 is lost with the progression of tumorigenesis long after exposure to the carcinogen. Thus, loss of heterozygosity of the ras gene appears to occur without multiple carcinogen-induced mutations, i.e., as a result of a cascade of events induced by an earlier ras mutation.

4NQO carcinogenesis: a mouse model of oral cavity squamous cell carcinoma.

BACKGROUND: A murine model of oral cavity carcinogenesis is needed to study the molecular aspects of malignant transformation. 4-Nitroquinoline-1-oxide (4NQO), a water-soluble carcinogen, produces squamous cell carcinoma in rodents. Protocols were designed to investigate the temporal aspects of neoplastic transformation. METHODS: 4NQO was applied topically to mouse palates for up to 16 weeks. Mice were observed and killed from 24 to 49 weeks. RESULTS: A spectrum of lesions ranging from atypia to moderately differentiated invasive squamous cell carcinoma (SCC) was produced. The severity of the lesions corresponded to the duration of treatment and the length of observation. There was no gross or microscopic evidence of an inflammatory reaction to 4NQO. The lesions were focal and normal mucosa predominated in the treated mice. CONCLUSION: 4NQO reliably produced preneoplastic and malignant oral cavity lesions, which morphologically and histologically mimic human head and neck cancer. Lesions develop long after 4NQO exposure and without an inflammatory response. Thus, the model should be useful for molecular analysis of neoplastic transformation.

Detection of epidermal growth factor receptor mRNA in tissue sections from biopsy specimens using in situ polymerase chain reaction.

Human epidermal growth factor (EGF) receptor mRNA was detected in cryopreserved tissue sections adherent to whole glass slides using in situ reverse transcriptase polymerase chain reaction. EGF receptor cDNA was synthesized in situ by reverse transcription using an EGF receptor-specific oligonucleotide primer. In situ polymerase chain reaction amplification in the presence of digoxigenin-11-dUTP and subsequent binding with an antidigoxigenin antibody conjugated to alkaline phosphatase allowed direct visualization. Because DNase, RNase, or proteinase K are not required, tissue integrity is maintained. EGF receptor mRNA is expressed in the basal layer of normal human skin epithelium and is significantly overexpressed in squamous cell tumor specimens, which is consistent with conventional analysis of EGF receptor expression. The assay is semiquantitative, quicker, more sensitive, and void of the nonspecific binding associated with in situ hybridization. In situ reverse transcriptase polymerase chain reaction using whole glass slides is ideally suited for detecting moderate to infrequently expressed transcripts in biopsy specimens.

Variation in cellular EGF receptor mRNA expression demonstrated by in situ reverse transcriptase polymerase chain reaction.

Cell to cell variation of epidermal growth factor (EGF) receptor mRNA levels in heterogeneous tissues has been demonstrated with an in situ assay that couples reverse transcriptase with the polymerase chain reaction (in situ RT-PCR). EGF receptor mRNA is consistently more highly expressed in regions where cell division occurs; EGF receptor mRNA is markedly reduced if not absent in areas of squamous cell differentiation. Both human and mouse tumors overexpress EGF receptor mRNA when compared to normal tissue. In situ RT-PCR performed on thin sections obtained from cell pellets of cultured cells with known levels of EGF receptor mRNA expression demonstrated that the mRNA detected is consistent with that observed by Northern analysis and quantitative PCR on isolated RNA and by protein levels detected by antibody binding assays. In situ RT-PCR is significantly more sensitive than in situ hybridization (ISH). The method avoids background associated with hybridization reactions as in ISH or ISH following in situ PCR. In situ RT-PCR appears to be applicable to any gene as long as the oligonucleotide primers used have been proven to be specific and effective in a standard RT-PCR assay.