Investigation of CPD and HMDS sample preparation techniques for cervical cells in developing computer-aided screening system based on FE-SEM/EDX.

This paper investigated the effects of critical-point drying (CPD) and hexamethyldisilazane (HMDS) sample preparation techniques for cervical cells on field emission scanning electron microscopy and energy dispersive X-ray (FE-SEM/EDX). We investigated the visualization of cervical cell image and elemental distribution on the cervical cell for two techniques of sample preparation. Using FE-SEM/EDX, the cervical cell images are captured and the cell element compositions are extracted for both sample preparation techniques. Cervical cell image quality, elemental composition, and processing time are considered for comparison of performances. Qualitatively, FE-SEM image based on HMDS preparation technique has better image quality than CPD technique in terms of degree of spread cell on the specimen and morphologic signs of cell deteriorations (i.e., existence of plate and pellet drying artifacts and membrane blebs). Quantitatively, with mapping and line scanning EDX analysis, carbon and oxygen element compositions in HMDS technique were higher than the CPD technique in terms of weight percentages. The HMDS technique has shorter processing time than the CPD technique. The results indicate that FE-SEM imaging, elemental composition, and processing time for sample preparation with the HMDS technique were better than CPD technique for cervical cell preparation technique for developing computer-aided screening system.

Specific intraepithelial localization of mast cells in differentiated vulvar intraepithelial neoplasia and its possible contribution to vulvar squamous cell carcinoma development.

AIMS: The aetiology of vulvar squamous cell carcinomas (SCC) that are not causally associated with high-risk human papillomavirus remains largely elusive. The aim of this study was to analyse the inflammatory response in its presumed precursor lesions, lichen sclerosus (LS) and differentiated vulvar intraepithelial neoplasia (dVIN), and provide evidence that dVIN is a likely precursor of vulvar SCC. METHODS AND RESULTS: Immunohistochemical analyses for CD4+, CD8+, CD20+, CD68+, S100+ and tryptase-positive immune cells were performed and quantified in LS (n = 7), dVIN (n = 19), SCC (n = 11), and normal vulvar tissue (n = 8). The subepithelial inflammatory response in dVIN and SCC was comparable, but absent in LS. Abundant intraepithelial mast cells were observed in dVIN only, and confirmed by electron microscopy, toluidine blue staining and cKIT expression. Adjacent keratinocytes displayed increased proliferation as determined by MIB-1 positivity. Electron microscopy revealed intraepithelial mast cell degranulation. Intraepithelial mast cells were not or infrequently observed in vulvar hyperplasia (n = 13), condylomata acuminata (n = 5), keratinocytic intraepidermal neoplasia of sun-exposed skin (n = 15), epidermal hyperplasia of head and neck (n = 12), and psoriasis (n = 3). CONCLUSIONS: These data indicate that dVIN can be recognized by intraepithelial mast cells and that they might promote the progression of dVIN to SCC.

Preneoplastic and neoplastic changes in the Leydig cells population in mice exposed to low doses of cadmium.

The morphological consequences of chronic exposition to low doses of cadmium (Cd) in the Leydig cells population were investigated in 40 sexually mature male mice at morphological and ultrastructural levels. Animals were orally exposed to cadmium (0.015 g/L of CdCl(2) in drinking water) for 3, 6, 12 and 18 months and then sacrificed, samples were collected for toxicological, light and electron microscope studies. Vascular lesions were evident from 6 months of Cd exposure, the severity of the morphological changes observed in the testicular vases were highly and clearly correlated to the time of exposure to Cd. The severity of the Leydig cells morphological changes were increasing along the time of exposure. Presence of cytoplasm vacuolization and degenerative images of the cells were frequent after 12 months of Cd exposure. Also two Leydig cells tumours after 12 and 18 months Cd exposure were presented. These results indicate that prolonged exposures to low doses of Cd are able to induce morphological damage on the Leydig cells.

[Helicobacter pylori infection and changes of cell gap junction of gastric epithelial cells in patients with gastric cancer and precancerous lesion].

OBJECTIVE: To observe the changes of cell gap junction ultrastructure of gastric epithelial cells in patients with gastric cancer(GC) and precancerous lesion(PL),and to investigate the relation between these changes and H.pylori infection. METHODS: Seventy patients with GC, 88 with PL, and 33 with chronic superfial gastritis (CSG) were studied. H.pylori was detected by rapid urease test,basic fuchsin stain and 14C-urea breath test. The CagA gene of H.pylori was determined by polymerase chain reaction(PCR).The cell gap junction ultrastructure was observed under transmission electronic microscope. RESULTS: Length of junction/unit perimeter of gastric epithelial cells in patients with PL was smaller than that in CSG patients, and the smallest width of the intercellular space was bigger than that in CSG patients. The number of cell junction, the number of junction/unit perimeter, and the length of junction/unit perimeter in patients with GC were all smaller than those in patients with CSG or PL, and its smallest width of the intercellular space was bigger than that in patients with CSG. In patients with GC, the number of cell junction, the number of junction/unit perimeter and the length of junction/unit perimeter in CagA+ H.pylori group were smaller than those in CagA(-) H.pylori group, and its smallest width of the intercellular space was bigger than that in CagA(-) H.pylori group. In PL patients, the intercellular space decreased, and the length of cell junction of gastric epithelial cells became bigger after H.pylori eradication. The length of junction/unit perimeter in patients of H.pylori eradication was bigger than that in patients without eradication, and the smallest width of the intercellular space was smaller than that in patients without eradication. CONCLUSION: The changes of cell gap junction of gastric epithelial cells in patients with GC and PL are associated with H.pylori infection especially CagA+ H.pylori infection. Eradication of H.pylori can promote the formation of cell junction.

A scanning electron microscopic study of the dysplastic epithelia adjacent to oral squamous cell carcinoma.

By light microscopy, the dysplastic oral epithelia due to the neoplastic processes are similar to epithelial changes due to the inflammatory processes. Scanning electron microscopy may elucidate the different surface changes between the two. The aim of this study was to examine the surface appearances of the dysplastic oral epithelia adjacent to oral squamous cell carcinoma to see if there are any surface changes. A total of 2 specimens, one specimen from each patient with oral squamous cell carcinoma, were used for this study. Each specimen was divided in two. One half was prepared for light microscopy and the other half was prepared for scanning electron microscopy. Light microscopically, the epithelia showed mild dysplasia. By scanning electron microscopy, the keratinized cells showed irregular microridges surrounding pits, which were variable and irregular in size and shape, and the nonkeratinized cells showed parallel microridges with irregularly widened intervals between each microridge. Irregular, broad, and partly swollen microridges and irregular short, stubby surface projections were also seen. The oral epithelia adjacent to oral squamous cell carcinoma showed mild dysplasia light microscopically but appeared abnormal by scanning electron microscopy. The abnormal epithelial cells showed pleomorphism, irregular and disoriented microridges, and abnormal surface microstructures.

Nuclear morphometry in columnar cell lesions of the breast: is it useful?

AIMS: To evaluate the nuclear morphometric features of breast columnar cell lesions (CCLs) observed on mammotome core biopsies, to determine if there are significant measurable differences between those with atypia and those without. Correlation with follow-up open excision specimens was made. METHODS: Mammotome core biopsies performed on patients that contained CCLs were derived from the departmental case files. Histological material was reviewed and foci of CCLs demarcated for nuclear morphometric assessment, which was accomplished using an imaging system. Nuclear parameters studied were nuclear area and perimeter, circularity factor and feret's diameter. Statistical analysis used the GraphPad Prism software, with p<0.05 indicating significance. RESULTS: On examination of core biopsies of 40 patients with CCLs, 8 lesions were benign, 4 showed atypical lobular hyperplasia, 8 showed CCLs with nuclear atypia, 19 disclosed atypical ductal hyperplasia (ADH) and 1 showed ductal carcinoma in situ (DCIS). The nuclear area, perimeter and feret's diameter of CCLs with atypia were significantly greater than those without (p = 0.04, 0.03 and 0.019, respectively), whereas no difference was observed in the circularity factor. Follow-up open excision biopsy specimens in 24 patients showed upgrading to DCIS in 40% of cases diagnosed initially with ADH on core biopsy compared with 20% of CCLs with atypia. CONCLUSIONS: Nuclear morphometry in CCLs confirms nuclear size as the key parameter in the assessment of nuclear atypia. Whether it can be potentially used as an adjunctive tool depends on the establishment of appropriate cut-offs.

Performance analysis of different wavelet feature vectors in quantification of oral precancerous condition.

This paper presents an automatic method for classification of progressive stages of oral precancerous conditions like oral submucous fibrosis (OSF). The classifier used is a three-layered feed-forward neural network and the feature vector, is formed by calculating the wavelet coefficients. Four wavelet decomposition functions, namely GABOR, HAAR, DB2 and DB4 have been used to extract the feature vector set and their performance has been compared. The samples used are transmission electron microscopic (TEM) images of collagen fibers from oral subepithelial region of normal and OSF patients. The trained network could classify normal fibers from less advanced and advanced stages of OSF successfully.

Chromosome changes associated with the progression of cell lines from preneoplastic to tumorigenic phenotype during transformation of mouse salivary gland epithelium in vitro.

Two mouse salivary gland epithelial cell lines, CSG 211 and CSG 205/2B1, isolated during carcinogen-induced neoplastic transformation in vitro, were analyzed cytogenetically before and after they acquired the ability to produce carcinomas in syngeneic animals. With the use of Giemsa banding techniques, chromosome changes were identified that were associated with the transition from a preneoplastic to a fully transformed (tumorigenic) phenotype during serial passage in vitro. Results were compared with those from a third cell line of similar origin, CSG 225, which was tumorigenic at the earliest passage tested. These cell lines were found to be subtetraploid, which confirms previous data, and the tumorigenic lines showed consistent losses of copies of chromosomes 1, 4, 7, 9, and 14. Compared with their preneoplastic counterparts, the loss of no single chromosome seems to be sufficient to generate the tumorigenic phenotype, but the loss of a combination of some or all of these chromosomes appears to be important in the phenotypic transition. In CSG 211 the loss of chromosome 7 is probably more important in this respect than loss of the other chromosomes listed. The karyotype of this cell line undergoes major structural rearrangement, which suggests that loss of specific regions of chromosomes 1 and 9 is also important.

Hyperplastic foci in precancerous rat liver: light microscopic and electron microscopic study.

4-Dimethylaminoazobenzene was fed to Wistar-derived, male, albino rats after hepatic siderosis had been induced by including ferric citrate in the diet. Iron-free foci of hepatocytes developed and this characteristic enabled them to be recognized macroscopically in the brown parenchyma. Five such lesions, each 1 mm or less in diameter, were studied by light and electron microscopy. The cells in the foci were larger than those surrounding the foci and had a granular and moderately basophilic cytoplasm. Ultrastructurally, the cells closely resembled normal hepatocytes. They possessed well-developed rough endoplasmic reticulum, numerous free ribosomes, peroxisomes, bile canaliculi, and cytoplasmic junctional complexes, but only small stores of glycogen were observed. Occasional ferritin-laden lysosomes persisted in some cells. These foci were regarded as hyperplastic. Possibly, they evolved into hyperplastic nodules either of the basophilic or vacuolated type. These foci should be clearly distinguished from hyperbasophilic foci that consisted of very poorly differentiated cells.

Activation of intracisternal A particles in mouse liver by diethylnitrosamine.

Livers of 6- to 7-week-old male C3H/He, CBA, A, and BALB/c mice were examined by electron microscopy for the presence of intracisternal A particles (ICAP) after administration of diethylnitrosamine (DEN) in drinking water. In control mice, ICAP were extremely rare; they were found in the livers of only 2 mice (strains C3H/He and A; none in the other strains). By contrast, the treatment of mice with DEN greatly enhanced the appearance of ICAP in the liver cells of all strains. Within 2 weeks of the treatment, ICAP were found in 8-26% of liver cells examined in all mice and the number of ICAP/cell ranged from 3 to 12. Aside from mild disorganization of the rough endoplasmic reticulum, such as segmentation and vesiculation, liver cells of carcinogen-treated mice showed none of the consistent abnormalities that characterize the appearance of ICAP. The reactivation of ICAP (which are usually suppressed in adult mice) by DEN may become a useful marker for analysis of the sequential alterations of the liver that lead to the development of hepatoma during carcinogenesis.

Surface structure of fetal rat brain cells during neoplastic transformation in cell culture.

The surface microstructure of fetal rat brain cells undergoing neoplastic transformation in long-term cell culture after a single transplacental pulse of 75 microgram N-ethyl-N-nitrosourea/g body weight to the fetal (18th day of gestation) BD IX rat was investigated by scanning electron microscopy. After about 3 weeks of culture, N-ethyl-N-nitrosourea-pretreated fetal rat brain cells showed focal proliferation of neural cells on an underlayer of flat, epithelioid cells. The neural cells exhibited varying forms of numerous dorsal ruffles and an increased number of other surface microprojections. Between the 40th and the 100th day, nodules of bipolar and multipolar neural cells were observed with a complex surface microstructure including many blebs and ruffles and an increased number of microvilli. After 100-210 days, more rapidly proliferating, morphologically altered cells formed "piled-up" foci, which resulted in a homogeneous population of cells with numerous long microvilli, large ruffles, and blebs over the whole surface. The cells retained the same altered surface structure until tumorigenicity after reimplantation into the syngeneic host was first observed (approximately 273 days). Surface alterations characteristic of the neoplastic cells were thus observable more than 100 days before the cells became tumorigenic.

Ultrastructural study of the normal mucosa-adenoma-cancer sequence in the development of familial polyposis coli.

Ultrastructural changes that occurred in the colon epithelia of patients with familial polyposis coli were investigated. Criteria of gradation of the crescendo changes from the mucosa in the controls, through the "normal" mucosa between polyps and adenomas in various stages of dedifferentiation, to invasive carcinoma were established. Our criteria were based on the following requirements: a) vesiculation and increasing numbers of small electron-dense bodies (secretory granules) and lysosomes in the mature and immature absorptive cells, b) presence of immature and undifferiated cells, c) variation in the globlet cells and appearance of atypical secretory cells, and d) nuclear changes. The results illustrated the adenoma-carcinoma sequence and added strong evidence to support its occurrence. Furthermore, this ultrastructural study revealed cellular changes that preceded adenomatous growth and may be of value as markers of early stages of cancer. However, this study also revealed a close link between the function and morphology of the mucosal epithelium.

Sequential morphologic changes during methapyrilene-induced hepatocellular carcinogenesis in rats.

The pathogenesis of hepatocellular tumors induced in F344 rats by the antihistaminic methapyrilene was investigated by light and electron microscopy in a serial sacrifice study. Eosinophilic foci of altered hepatocytes were found in portal areas after 1 week of treatment, the eosinophilia being caused by proliferation of mitochondria. Eosinophilic neoplastic nodules developed from such lesions after 16 weeks of treatment. Hepatocellular carcinomas developed after 26 weeks of treatment. Mitochondrial proliferation, which had been found as a marker for hepatocytes altered by this compound at 1 week of treatment, was still present in the hepatocellular carcinomas, which therefore met the morphologic criteria of oncocytomas.

Three-dimensional analysis of isolated hexosaminidase-altered aberrant crypts from colons of 1,2-dimethylhydrazine-treated rats.

Aberrant crypt foci, consisting of morphologically irregular crypts, are thought to be precancerous lesions for colorectal cancers. For analysis of individual crypts, F344 rats were administered weekly subcutaneous injections of 1,2-dimethylhydrazine ten times and sacrificed at experimental weeks 10 and 20 with 5-bromo-2'-deoxyuridine (BrdU) incorporation 1 h before the sacrifice. Isolated colonic crypts were classified into hexosaminidase-altered aberrant crypts (HAACs) and hexosaminidase-preserved normal-appearing crypts (HPNCs) and stereopaired images (tilt angle, 6 degrees ) were taken with a scanning electron microscope for three-dimensional analyses. While HPNCs showed symmetrical fission at the base, HAACs exhibited abnormal budding in the middle of the crypt body. At week 10, average BrdU labeled cells per crypt for DMH-treated HPNCs and HAACs were 4.9 +/- 1.0 and 18.7 +/- 2.2 (P < 0.0001), respectively, while the value for non-treated control crypts was 14.7 +/- 0.8/crypt. BrdU-positive cell numbers per unit crypt length (100 microm) in HPNCs and HAACs were 1.75 +/- 0.37 and 5.99 +/- 0.70 (P < 0.0001), respectively, while that for the control was 6.65 +/- 0.35 (P < 0.02 vs. HAAC). At the 20-week time point, the numbers per crypt were 4.0 +/- 0.8, 10.1 +/- 1.6, and 27.4 +/- 2.4, respectively, the control value being significantly higher than the others (P < 0.0001). The figures per unit length were 1.72 +/- 0.35, 2.92 +/- 0.42, and 13.39 +/- 1.11 (P < 0.0001 vs. HAAC and HPNC), respectively. BrdU incorporating cells were distributed in the bottom third of the crypt columns in HAACs, but only 18% in the HPNCs, providing evidence of hyperplasia. HAACs could be good surrogate indicators of carcinogen exposure, at least some of which may be related to colon carcinogenesis.

Overexpression of int-5/aromatase in mammary glands of transgenic mice results in the induction of hyperplasia and nuclear abnormalities.

Our recent studies have shown that the cellular gene at the mouse mammary tumor virus integration site in the int-5 locus is aromatase. To study the role of int-5/aromatase in normal mammary development and mammary neoplasia, we have generated transgenic mice that overexpress int-5/aromatase under the control of mouse mammary tumor virus enhancer/promoter. All the transgenic virgin (n = 10) and postlactational (n = 15) females that overexpress int-5/aromatase show various histological abnormalities. Overexpression of int-5/aromatase in mammary glands of virgin females leads to the enlargement of 40% of ducts, of which 65% had hyperplastic lesions, 20% had dysplastic lesions, and 15% had fibroadenoma lesions. Overexpression of int-5/aromatase in involuted mammary glands of transgenic females induces hyperplasia in 75-80% of ducts and glands that exhibit a range of morphological abnormalities, including formation of hyperplastic alveolar nodule (10%), ductal and glandular hyperplasia (70-80%), ductal and lobular dysplasia (15%), and nuclear abnormalities (2-5%) such as multinucleation and karyomegaly, which are all indicative of preneoplastic changes. Our results show that early exposure of mammary epithelium to in situ estrogen and continued exposure to in situ estrogen as a result of overexpression of int-5/aromatase appears to predispose mammary tissue to preneoplastic changes, which may, in turn, increase the risk of developing neoplasia and increase susceptibility to environmental carcinogens. These findings support clinical and experimental data that suggest that early estrogen exposure increases breast cancer risk.

Distinction between preneopastic and neoplastic mammary cell populations in vitro by cytochalasin B-induced multinucleation.

Epithelial cell cultures of normal mammary gland, preneoplastic hyperplastic nodule outgrowth lines, primary tumors, and transplanted tumors, all derived from BALB/c mice, were examined for their response to cytochalasin B to determine if cells of primary mammary tumors multinucleated and if preneoplastic hyperplastic alveolar nodule cells responded differently than cells of primary tumors. Established tumorigenic and nontumorigenic cell lines were also examined as positive and negative controls. The standard assay conditions were optimized at 1 microgram CB per ml for 48 hr. The results, expressed as the mean percentage of cells exhibiting three or more nuclei per cell were: normal mammary cells, 5%; preneoplastic mammary cells, 4%; primary mammary tumor cells, 36%; transplanted mammary tumors, 70%; tumorigenic established cell lines, 80%; and nontumorigenic established cell lines, 5%. The frequency of tumor cells exhibiting multinucleation increased with serial transplantation in vivo and with serial passage in vitro. The results demonstrate that neoplastic cells within a primary tumor exhibit uncontrolled nuclear division and that uncontrolled nuclear division is a distinguishing characteristic between preneoplastic and neoplastic mammary cells.

Microtubules and actin-containing filaments of normal, preneoplastic, and neoplastic mouse mammary epithelial cells.

The distribution and organization of microtubules (MT's) and actin-containing microfilaments (MF's) were examined in epithelial cells of primary cultures established from normal, preneoplastic, and neoplastic mouse mammary tissues and in cells of three clonal culture lines derived from murine mammary adenocarcinomas. No consistent differences in the cytoskeletal components were found among cell populations of the primary cultures as revealed either by indirect immunofluorescence using antibodies to tubulin and actin or by electron microscopy. Overall, the majority of cells in the three types of primary cultures possessed elaborate complexes of MT's and actin filaments after fluorescent staining with the appropriate antibodies, and abundant MT's and MF's were found in the cells at the ultrastructural level. Similar patterns of MT's and MF's were observed in cells of two of the clonal mammary tumor lines. Cells of the third line, however, exhibited intricate networks of MT's but had a reduction in actin cables detectable by the immunofluorescence procedure. Moreover, MF's were difficult to locate by electron microscopy. The results suggest that the lesion(s) in growth control in the neoplastic mammary cells may not involve any gross alterations in MT's or MF's.

Changes in peroxisomes in preneoplastic liver and hepatoma of mice induced by alpha-benzene hexachloride.

Peroxisomes in hepatomas and hyperplastic preneoplastic liver lesions induced in mice by 500 ppm alpha-benzene hexachloride were examined histochemically and electron microscopically. Although most of the hepatomas were well-differentiated tumors and contained a considerable number of peroxisomes, the tumor cells did not respond to ethyl-alpha-p-chlorophenoxyisobutyrate with proliferation of peroxisomes. At the 16th week of carcinogen feeding, hyperplastic nodules appeared and advanced to further stages. A majority of the nodules showed a considerable number of peroxisomes and the inductive proliferation of peroxisomes. Within the nodules, foci of proliferation of the cells that showed no inducibility of proliferation of peroxisomes appeared. These cells proliferated further, replacing the most part of the nodules, and with this process hepatomas appeared to have been formed. No abnormal matrical inclusions of peroxisomes were formed in the cells of hyperplastic nodules by ethyl-alpha-p-chlorophenoxyisobutyrate unlike in the case of rats.

Chemopreventive effects of dietary D,L-alpha-difluoromethylornithine, an ornithine decarboxylase inhibitor, on initiation and postinitiation stages of diethylnitrosamine-induced rat hepatocarcinogenesis.

The modifying effects of dietary administration of D,L-alpha-difluoromethylornithine (DFMO) during initiation or postinitiation phase on the hepatocarcinogenesis initiated by diethylnitrosamine (DEN) were investigated in male F344 rats. A total of 129 animals were divided into seven groups. Groups 1-5 were given the drinking water containing 40 ppm DEN for 5 weeks, starting at 7 weeks of age. Groups 2 and 3 were fed the diets mixed with 500 and 1000 ppm DFMO, respectively, for 7 weeks, starting at 6 weeks of age. Groups 4 and 5 were given the diets containing 500 and 1000 ppm DFMO, respectively, starting 1 week after DEN exposure and maintained on these diets until the end of the study (Week 32). Rats in group 6 were fed the DFMO diet (1000 ppm) alone during the experiment. Group 7 served as an untreated control. At the end of the study, the incidences of liver cell foci (resistant iron accumulation or positive for glutathione S-transferase placental form) and hepatocellular neoplasms along with polyamine levels in the liver were measured. Also, morphometric analysis of silver-stained nucleolar organizer regions proteins as cell proliferation activity in liver cells was performed. The mean incidences and areas of foci in rats given DEN and DFMO in groups 2-5 were significantly lower than those of group 1 (P < 0.01). The frequencies of liver cell tumors in group 3 (50%), 4 (24%), and 5 (45%) were significantly reduced compared to that of group 1 (100%) (P < 0.01). The multiplicities of neoplasms in group 2 (1.15/rat), 3 (0.65/rat), 4 (0.35/rat), and 5 (0.95/rat) were significantly smaller than that of group 1 (3.34/rat) (P < 0.001). Although the polyamine levels of liver tissues among the groups showed no clear differences among the groups, the number and area of silver-stained nucleolar organizer regions proteins/nucleus in rats given DEN and DFMO (groups 2-5) were significantly lower than those of group 1. These results indicate that the feeding of DFMO during the initiation or postinitiation stage clearly inhibited DEN-induced rat hepatocarcinogenesis and that such inhibition may be due to alteration in cell proliferation activity caused by DFMO.

Epidermal ribosome accumulation during two-stage skin tumorigenesis.

The increase in interfollicular epidermal ribosomes on the backs of mice initiated with 7,12-dimethylbenz(a)-anthracene and promoted with 12-0-tetradecanoyl-phorbol-13-acetate was disproportionate to the increase in epidermal wet weight, protein, and DNA. Whereas ribosome numbers increased five- to sixfold 48 hr after the first, fourth, or eight application of 12-3-tetradecanoyl-phorbol-13-acetate, epidermal tissue increased only two- to threefold at these times. This disproportionate increase was due to the fact that, concurrent with the increased amount of interfollicular epidermal tissue and cells, ribosomes per g epidermis and per mg DNA increased two to three times normal. The tissue concentration and cellular content of ribosomes were also increased in the epidermal component of induced squamous papillomas. The work of others has demonstrated that, during growth of other tissues and organs, ribosome accumulation is proportionate to accumulation of tissue and/or cells. The results of our study indicate that the epidermis may have unique kinetics of ribosome accumulation during induced growth. Furthermore, these findings suggest the interesting possibility that other tumor-prone surface epithelia, such as the linings of the respiratory and gastrointestinal tracts, have similar kinetics of ribosome accumulation during induced growth.