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This study examined the effects of variety and quantity of dietary fat consumed by rats during pregnancy and lactation on female offspring's response to chemically induced mammary cancer. Groups of six female rats were fed diets containing 7% corn oil (7-CO), 15% CO (15-CO), 7% olive oil (7-OO), or 15% OO (15-OO) for 5 wk prior to, and during, pregnancy and lactation. Female offspring (n = 15 per group) were fed a 7-CO diet, and mammary cancer was induced with 7,12-dimethylbenz[a]anthracene (DMBA). Three months following cancer induction tumor incidence and size were recorded, and markers of apoptosis, serum estrogen concentrations, and hepatic phase II enzymes were measured. Tumor incidence was 47% in offspring born to mothers fed the 7-OO diet, rose to 67% in 7-CO and 15-OO offspring, and reached 86% in 15-CO. A trend toward smaller tumors was observed in the 7-OO group, and offspring of mothers fed high-fat diets had significantly more tumors. Estradiol levels at the end of lactation were significantly lower in mothers fed 7-OO but were similar in all groups of offspring. In tumor tissue, Bcl-2 expression was highest in the 15-CO offspring, and Bak expression was significantly higher in rats exposed to OO. A distinct trend toward increased caspase-3 expression (20 kDa) was observed in the 7-OO offspring, and both low-fat diets significantly elevated caspase activity. In healthy mammary tissue, rats exposed to low-fat diets had significantly higher caspase-3 (32-kDa) levels, and caspase-3 activity was significantly higher in the healthy tissue from both OO groups. Hepatic quinone reductase activity was significantly lower in offspring of mothers fed the low-fat diets. These results indicate that perinatal exposure to OO may have a protective effect against future development of mammary cancer in female offspring, whereas high-fat diets fed to pregnant and lactating rats, in particular CO, may be deleterious. [ABSTRACT FROM AUTHOR]

Two-year-old mice of the long-living transgenic mice of the alphaMUPA strain were previously found to show higher tumor resistance than the their initial wild-type (WT) strain (Tirosh, 2003). To better understand the mechanism underlying the differences in tumorigenesis rates between the two mouse lines, the rate of tumorigenesis and survival effects were studied in alphaMUPA mice and parental WT mice exposed to dimethylbenz(a)anthracene (DMBA). Each animal received three intragastric feedings of DMBA, each one week apart, at doses of 2, 1, and 1 mg dissolved in 0.2 ml corn oil; thus, the total amount of the carcinogen was 4 mg/mouse. Control mice received corn oil. The alphaMUPA mice exhibited distinctly higher survival rates in experimental chemically-induced tumorigenesis compared to their WT counterparts: 93% vs. 67%, p =2.7. The rate of tumorigenesis differed between the mouse lines (yield was 1.5 and 2.1), owing to a distinct tendency toward decreased tumor frequency in the skin and forestomach in the alphaMUPA mice. The experimental duration was also significantly higher for transgenic mice: 35.9 +/- 1.2 weeks compared to 30.5 +/- 1.3 weeks in WT mice, p <0.01. The lungs, forestomach and skin were target organs for the carcinogenic effect of DMBA. Our observations suggest that aging promotes the rate of spontaneous and induced tumorigenesis.

The potential preventive effect of the synthetic pineal peptide Epitalon (Ala-Glu-Asp-Gly) on spontaneous tumorigenesis in mice was studied. One-year-old female C3H/He mice were kept for 6.5 months under standard conditions. Epitalon was injected at a dose of 0.1 microg, 5 times a week. Long-term exposure to Epitalon in small doses did not show any toxic effect. Treatment with Epitalon decreased the number of tumor-bearing mice with malignant tumors and prevented the development of metastases. Spontaneous tumors of the reproductive organs (mammary glands and ovaries) were predominant in both groups of mice (control and experimental). The mammary gland tumors were different variants of invasive ductal carcinomas. In the ovaries, granulosa-cell tumors were found. Tumors were in the minority in other organs and had benign characteristics. In control mice, metastases were found in 3 out of 9 tumor-bearing mice, all of them being from tumors of the reproductive organs. Treatment with Epitalon slowed down the development of metastases from spontaneous tumors, and no metastases were found in the experimental mice. These data highlight the antimetastatic effect of Epitalon as part of its oncostatic properties.

We analyzed the morphological changes accompanying the development of cancer in the mouse forestomach. The main aim of the study was to evaluate whether cancer in this area of the stomach arises de novo or undergoes a series of precancerous changes. Tumors were induced by the 1,2-dimethylbenz(a)antracene (DMBA) at a total dose of 4 mg/mouse. The suspected areas of the stomach were studied morphologically in 79 mice. Benign tumors (squamous-cell papillomas) and malignant tumors (squamous-cell carcinomas) were found in 40 mice. Tumors arose in all cases together with differential changes in the forestomach epithelium. These changes were seen as irregular diffuse hyperplasia or focal proliferation, with or without differential signs of dysplasia. Destruction of the basal epithelial membrane indicated transformation of the process into malignant invasive carcinoma. Thus, in chemically induced cancer of the forestomach, squamous-cell carcinoma develops as the final stage of morphologically recognizable precancerous changes in the epithelial layer. De novo formation of such tumors in the forestomach was not observed.

In our previous studies, we showed that soluble tumor-associated antigens (sTAA) of 66 kDa and 51 kDa have distinct tumor-preventive effects on chemically induced mammary cancer in rats and are able to repair the damage caused by tumorigenesis in its early stages. In the present study, we investigated whether these proteins can prevent the development of chemically induced tumors in mice. The study was performed on C3H/He mice which have the ability to develop many spontaneous tumors with age. Forty-four, 6-week-old mice were exposed twice at a 2-week interval to the carcinogen 9,10-dimethyl-1,2-benz(alpha)anthracene (DMBA), at a dose of 2 mg/mouse administered intragastrically. Two months later, the mice were divided into two groups. One group received sterile saline twice a week at a dose of 0.2 ml/mouse, intraperitoneally (i.p.). The other group received sTAA twice a week at a dose of about 10 microl in 0.2 ml of sterile saline/mouse, i.p. Periodically, all mice were checked for the presence of tumors. The experiment was terminated at week 35. Vaccination with sTAA increased the time of involvement of mice in the experiment, prevented the tumorigenic effect of DMBA, and inhibited further development of existing tumors.

Previously, we showed that the 66 and 51 kDa soluble tumor-associated antigens (sTAAs) have distinct suppressive effects on chemically induced mammary cancer in rats, both alone and in combination with the hormone-related anticancer drug tamoxifen. Here, we describe the effects of both sTAA and tamoxifen on the histological structure of ovaries in mammary tumor-bearing 30- to 34-week-old rats. Central ovary sections were pooled, the number of the healthy and degenerated follicles were counted, and the size of the corpora lutea was estimated. In follicular development primordial, primary, preantral and antral stages were recognized. Only healthy follicles with visible nuclei were counted. Follicular degeneration was estimated as the number of atretic follicles with follicular remnants. Treatment with tamoxifen alone or in combination with sTAA significantly increased the number of primordial follicles and atretic follicles in the ovaries, and promoted the formation of small follicular cysts. Total area of the corpora lutea decreased. sTAA participated in this process by increasing apoptosis in degenerated follicles.

This study examined whether soluble 66 and 51 kDa tumor-associated antigens (sTAA), isolated from the serum of rats with mammary cancer, possess specific suppressive effects on chemically-induced mammary tumorigenesis in syngeneic counterparts. Dimethylbenzanthracene (DMBA, 10 mg/rat, two administrations) was used to induce mammary tumors in 8-week-old Sprague Dawley rats. After the appearance of numerous tumors, preparations of sTAA (50 to 60 microg/rat in 0.5 ml sterile PBS) obtained from breast cancer patients (heterologous sTAA) or from syngeneic mammary tumor-bearing rats (syngeneic sTAA) were administered weekly for 12 weeks. The following groups of mammary tumor-bearing rats were studied: groups 1 and 3, control rats treated with saline; group 2, rats treated with heterologous sTAA; and group 4, rats treated with syngeneic sTAA. The experiment was terminated when tumors in 50% of the rats became ulcerous. The treatment with both types of sTAA significantly decreased, compared to controls and initial values, the yield and total area of the tumors. We conclude that syngeneic sTAA have tumor-suppressive properties, which are very similar to those in heterologous sTAA.

We showed previously that soluble tumor-associated antigens (sTAA) isolated from breast cancer patients could suppress chemically-induced tumorigenesis in rats in comparison to the effect of commercial human albumin (CHA). Herein we analyze the possible mechanism of those findings. The following groups of mammary tumor-bearing rats were used in the studies: i) control rats treated with saline; ii) rats treated with CHA; and iii) rats treated with human sTAA. Different zones of the spleen, regional lymph nodes and tumors and their cellular content (B and T cells) were analyzed using the methods of morphometry and immunohistochemistry. Treatment of tumor-bearing rats with CHA resulted in a significant decrease in the size of the germinal center of the follicles. The number of B lymphocytes in the mantle layer of the follicles, the marginal zone and red pulp decreased significantly. The number of CD8+ T cells also decreased in the marginal zone and red pulp, whereas the number of CD4+ T cells increased in the periarterial lymph sheath (PALS) and the red pulp. Reaction of the spleen to vaccination with sTAA manifested in a significant increase in the size of most areas of the white pulp and in the number of B lymphocytes. In lymph nodes from control rats or those treated with CHA, CD8+ lymphocytes mainly accumulated in the paracortical zone. In rats treated with sTAA, CD8+ lymphocytes accumulated also in the medulla. The number of CD4+ T cells in these rats sharply increased and accumulated mainly in the medulla around the vessels. The total number of lymphocytes was changed differently in different areas of tumors (peripheral vs. at depth). The number of CD8+ cells significantly increased at depth of tumors, and also the ratio in the number of these cells at depth of tumors compared to a periphery increased. No difference was found in response of lymph cells to different types of treatment. All findings indicated a strict antitumor effect of vaccination with the sTAA, which prevents the development of insufficiency of the immune system when an intensive immune reaction takes place.

We analyzed the role of T- and B-lymphocytes in the antitumor effects of the anticancer drug tamoxifen and soluble tumor-associated antigens (sTAA) on rat mammary carcinogenesis. Studies were performed on the spleen from the following groups of mammary tumor-bearing rats. i) Rats in group 1 were not exposed to DMBA and served as age-related controls. Rats in other groups were exposed to DMBA and received different types of treatment; ii) rats in group 2, received no additional treatment, and served as carcinogen-related controls; iii) rats in group 3 were treated with the commercial hormone-dependent anticancer drug tamoxifen by weekly subcutaneous (s.c.) injections of 10 mg dissolved in 0.5 ml distilled water per rat; iv) rats in group 4 were vaccinated s.c. weekly with a preparation of sTAA (50 micro l/rat) dissolved in 0.5 ml of phosphate-buffered saline; v) rats in group 5 were treated with tamoxifen and were also vaccinated with a preparation of sTAA. Different zones of the spleen were measured and their T- and B-cell contents were analyzed immunohistochemically. The treatment with tamoxifen significantly increased the total number of lymphocytes in the follicles, PALS (periarterial lymph sheath) and red pulp relative to all other groups. The combined treatment with tamoxifen and sTAA increased the areas of white pulp, the PALS, and marginal zone. The number of B-cells was higher in the marginal zone of spleens from age-related controls, as well as from rats treated with sTAA and those treated with tamoxifen and sTAA. The number of CD4+ lymphocytes in the PALS was higher in rats treated with sTAA and tamoxifen, and notably so in those treated with sTAA alone. The number of CD8+ lymphocytes was significantly lower in the PALS of spleens from all tumor-bearing rat groups compared to the unexposed age-related control rats. We suggest that the tumor-suppressive effect of sTAA and tamoxifen is accompanied by the activation of B- and T-lymphocyte production.

Caloric restriction (CR) is currently the only therapeutic intervention known to attenuate aging in mammals, but the mechanisms underlying this phenomenon are still poorly understood. To study this issue, the transgenic model of alpha MUPA mice, which previously were reported to spontaneously eat less and live longer compared with their wild-type (WT) control mice, were used. Currently, two transgenic lines that eat less are available, thus implicating the transgenic enzyme, that is, the urokinase-type plasminogen activator (uPA), in causing the reduced appetite. Recently, several changes in the alpha MUPA liver were noted, at the mitochondrial and cellular level, which consistently pointed to an enhanced capacity to induce apoptosis. In addition, alpha MUPA mice showed a reduced level of serum IGF-1 and a reduced incidence of spontaneously occurring or carcinogen-induced tumors in several tissues. Overall, the alpha MUPA model suggests that long-lasting, moderately increased apoptotic capacity, possibly linked in part to modulation of serum IGF-1 and mitochondrial functions, could play a role in the attenuation of aging in calorically restricted mice.

This study examined whether the soluble 66- and 51 kDa tumor-associated antigens (sTAA), isolated from the serum of breast cancer patients, possess specific suppressive effects on chemically-induced rat mammary tumorigenesis in comparison to commercial human albumin. Dimethylbenzanthracene (DMBA, 10 mg/rat, 2 administrations) was used to induce mammary tumors in 8-week-old Sprague Dawley rats. After the appearance of many large tumors, preparations of sTAA (50-60 micro g/rat in 0.5 ml sterile PBS) or commercial human albumin (HA, in the same doses as sTAA) were administered weekly, for 10-14 more weeks. The following groups of mammary tumor-bearing rats were studied: i) control non-treated rats, ii) rats treated with HA, iii) rats treated with sTAA. The experiment was terminated when tumors in 70% of the rats became ulcerous. The treatment with sTAA significantly decreased, compared to controls, the yield and total area of the tumors. In rats treated with sTAA, the appearance of new tumors stopped at week 5 as compared to week 7 in rats treated with HA and week 10 in control rats. In rats treated with sTAA, the time of appearance of ulcerous tumors increased to 8 weeks, as compared to 6 weeks in controls and in rats treated with HA. Duration of the experiment increased from 11 weeks in controls to 12 weeks in rats treated with HA and to 14 weeks in rats treated with sTAA. We conclude that sTAA have tumor-suppressive properties, which are well-defined if the treatment is begun on small tumors.

This study examined whether the soluble 66 and 51 kDa tumor-associated antigens (sTAA) could promote suppression by the anticancer drug 5-fluorouracil (5-Fu) of chemically induced mammary tumorigenesis, and which, if any, morphological changes in the immune organs accompany this treatment. Dimethylbenzanthracene (DMBA, 8 mg/rat, twice) was used to induce mammary tumors. After the appearance of many large tumors, the preparations of sTAA and 5-Fu, alone or in combination, were administered in weekly doses, for 4 weeks. The following groups of mammary tumor-bearing rats were studied: 1) control non treated rats, 2) rats treated with sTAA, 3) rats treated with 5-Fu, 4) rats treated with 5-Fu and sTAA. The experiment was terminated when tumors in 70% of control rats became ulcerous. Treatment with sTAA alone significantly decreased tumor yield and their total area relative to controls. Both of these parameters showed an even larger significant decrease after treatment with 5-Fu, and the most marked decrease was obtained after the combined treatment with 5-Fu and sTAA. Results demonstrated that not only do sTAA have tumor-suppressive properties, they also enhance the anticancer effects of 5-Fu and prevent its toxic side effects. Morphologically, the treatment with sTAA was manifested in a significant increase in the size of the spleen follicles and mantle layer compared to control rats with large tumors. The treatment with 5-Fu decreased the sizes of almost all areas of the spleen compared to control rats, whereas the combined treatment with 5-Fu and sTAA increased all these parameters to the levels found in rats treated with sTAA alone. The total areas of the cortex and paracortex in the lymph nodes increased after treatment with sTAA. Treatment with 5-Fu alone resulted in a significant decrease of these areas which, as seen in the spleen, increased after combined treatment with 5-Fu and sTAA. Similar changes were seen in the areas of the separate lymph node zones. We concluded that the addition of sTAA to conventional tumor chemotherapy regimens has a remarkable synergistic effect on mammary tumors leading to curative antitumor responses of the host's immune organs.

The effect of the synthetic pineal peptide Epitalon (Ala-Glu-Asp-Gly) on proliferative activity in colon tumors, and in mucosal epithelial cells adjacent to and located far from tumors was studied in rats. To evaluate the effect of Epitalon on different stages of carcinogenesis, different treatment regimens were used: during the tumor initiation stage, during the tumor-promotion stage, or during the entire process of tumor development. Eighty 2-month-old male LIO rats were exposed weekly to five subcutaneous injections of 1,2-dimethylhydrazine (DMH) at a single dose of 21 mg/kg body weight. Rats were divided into four groups. Control rats (group 1) received saline at a dose of 0.1 ml during the entire experiment. Rats in group 2 were treated with Epitalon at a dose of 1 micro g, five times a week, for 6 months, from the first injection of DMH till the end of the experiment. Rats in group 3 were treated with Epitalon after termination of the carcinogen injections. Rats in group 4 were treated with Epitalon only during the period of DMH exposure (for the first 5 weeks of the experiment). DMH induced proliferation of the secretory epithelium, and this phenomenon was accompanied by a decrease in the size of the stromal area and the area of lymph infiltration in colon tumors and in the colon mucosa adjacent to the tumors (group 1). Epitalon attenuated this effect, especially when the treatment was continued throughout the experiment (group 2). It increased the stromal areas, as well as that of lymphoid infiltration in the colon mucosa adjacent to the tumors. The intensity of lymphoid infiltration was activated in both the colon mucosa adjacent to a tumor and in the tumor. Mitotic activity of tumor cells was significantly inhibited by Epitalon when the treatment was given throughout the experiment (group 2). In parallel, a high level of apoptosis was seen in the same group. Thus, the strongest inhibitory effect of Epitalon on carcinogenesis in the colon mucosa was manifested when the treatment was continued throughout the experiment.

Caloric restriction (CR) can extend the life-span of multiple species and is the only intervention known to attenuate aging in mammals. Mechanisms mediating the CR influence are as yet unclear. To get insight into these mechanisms we took advantage of alphaMUPA transgenic mice that have previously been reported to spontaneously eat less and live longer compared with their wild-type (WT) control. Here we report that mitochondria isolated from young adult alphaMUPA livers showed increased susceptibility to calcium-induced high-amplitude swelling, increased cytochrome c release and enhanced glutathione levels. Furthermore, young adult alphaMUPA mice showed significantly enhanced caspase-3 activity in liver homogenates, increased fraction of apoptotic hepatocytes, and a lower level of serum IGF-1. In addition, alphaMUPA mice showed a decreased rate of spontaneously occurring lung tumors at an old age. Short-term (8 weeks) calorically restricted WT mice also showed an increase of mitochondrial swelling and caspase-3 activity compared with ad libitum (AL) fed WT mice. These results provide the first indication that CR can enhance mitochondrion-mediated apoptotic capacity. Collectively, the results are consistent with the possibility that long lasting, moderately increased apoptotic capacity, possibly linked in part to IGF-1 and GSH modulation, could play a role in the CR-induced anti-aging influence in mice.

We studied whether feeding pregnant female rats different high fat diets affects structural zones in the spleen and lymph nodes, involved in production of T and B cells, as well as cell kinetics and apoptosis in some offspring with mammary glands tumors. Rat mothers were fed either a 7% or 15% corn-oil or a 7% or 15% olive-oil diet. At four weeks of age, female offspring (n=10-15 per group) were transferred to 7% corn oil diet. Five-week old offspring were exposed twice to the carcinogen, dimethylbenz(a)antracene (10 mg/rat/week). Three months later, tumors were counted and sized, and samples from the spleen, axillary lymph nodes and tumors collected for immunohistochemical analyses. Feeding the mothers with both the 7% and 15% olive-oil diets significantly increased the number of tumor-free rats in offspring. Tumors were characterized with active mitosis, intensive lymphoid infiltration inside a knot and high rates of apoptosis, particularly in tumors obtained from rats whose mothers were fed the 15% olive-oil diet. In the spleen, the 15% olive-oil diet significantly increased the areas of the follicles and germinal centers but only in tumor-free rats. In tumor-bearing rats, areas of germinal centers increased compared to the 7% olive-oil diet. The 15% olive-oil diet increased all areas of the lymph nodes in tumor-free rats, while in tumor-bearing rats, this diet increased the areas of the cortex and mantle layer. We conclude that exposure to various diets in utero and during lactation affects the immune system. In addition, the promotion of apoptosis may play a key role in the mechanisms involved in the transplacental effects on mammary tumor development as seen using a 15% olive-oil diet, similar to the high fat diets of Mediterranean countries.

The aim of this review was to analyze the role of cell kinetics and apoptosis in the cellular mechanism underlying the effects of soluble tumor-associated antigens (sTAA) on chemically-induced mammary cancer in rats treated with the anticancer drug cyclophosphamide (CPA). Mammary gland cancer was induced with dimethylbenz(a)anthracene (DMBA), and tumors, the spleen, thymus, bone marrow and lymph nodes were studied by morphometric and immunohistochemical methods. We suggest that inhibition of the functional activity of the immune system is one of the main reasons for the toxic effects of CPA, and that the tumor-suppressive antitoxic effects of sTAA result from their activation of T-lymphocyte production in this system, particularly in the spleen and lymph nodes. The results of our experiments have shown that vaccination with sTAA actively promotes generation of the host's antitumor immune response. This is manifested in inhibited proliferative activity of the tumor cells, stimulated production of T lymphocytes and an increased rate of apoptosis among tumor cells.

The aim of this study was to analyze the roles of proliferative activity, lymphoid infiltration and apoptotic rate in the cellular mechanism underlying the promotion effects of soluble tumor-associated antigens (sTAA) in mammary cancer in rats treated with the anticancer drug cyclophosphamide (CPA). Studies were performed on the following groups of rats: i) control tumor-bearing rats, ii) tumor-bearing rats treated with sTAA, iii) tumor-bearing rats treated with CPA, iv) tumor-bearing rats treated with CPA and sTAA. Mammary gland cancer was induced with dimethylbenz(a)anthracene (DMBA), and the rate of lymphoid infiltration, T cell content (CD4+ and CD8+ cells), and mitotic and apoptotic indices in tumors were evaluated. In control tumor-bearing rats, high lymphoid proliferation, as well as a high number of CD8+ cells, was found in tumors. Treatment with sTAA further significantly increased the total number of lymphoid cells and the number of CD8+ lymphocytes. CPA sharply decreased the production of all lymphoid cells studied, especially of CD4+ lymphocytes. The combined treatment of CPA and sTAA increased the number of lymphoid cells, although they did not reach control levels. The mitotic index significantly decreased as a result of the treatment with CPA alone and especially after the combined treatment with CPA and sTAA. The results of our experiments demonstrate that vaccination with sTAA actively promotes the generation of the host's antitumor immune response. This is manifested in inhibited proliferative activity of tumor cells, stimulated production of T lymphocytes and increased rate of apoptosis among tumor cells.

The objective of this study was to examine whether splenectomy alters the tumorigenic response of rats to chemically-induced mammary tumors and to determine the role played by the parathymic lymph nodes (PTLN) in the antitumor immune response. Female rats were splenectomized and then exposed to 9,10-dimethyl-1,2-benz(a)anthracene (DMBA) to induce mammary tumors. Splenectomy decreased the rate of tumor appearance. The latent period for appearance of the first tumors in splenectomized rats was 12.0 +/- 0.9 week compared to 9.7 +/- 0.5 week in intact controls. The latent periods for appearance of all tumors including those with malignancy were similar for both rat groups. Splenectomy caused a significant increase in the size of the PTLN as well as changes in their structure. The cortex became thick, better formed and enriched with lymph elements of follicles and a wide venous net. CD8+ cells infiltrated the paracortex whereas CD4+ cells were located around the blood vessels. In conclusion, splenectomy inhibits the early stages of tumorigenesis, but does not prevent the progress of carcinogenesis. Different responses of splenectomized (operated) and intact rats to the effect of DMBA can be explained by an increase in the nonspecific resistance of splenectomized rats as a result of the operation. PTLN actively participate in this compensatory reaction of the immune system of animals.

There is increasing evidence that tumors express putative target molecules in a therapeutic immune reaction. Identification of immunogenic tumor-associated antigens (TAA) may enable the development of new modes of vaccination with the addition of immunotherapy as a potentially powerful weapon in the fight against cancer. In the present review, the authors' observations on the role of the soluble low-molecular-mass heat shock proteins and tumor-associated antigens, named as a complex of STAA, in the prevention and therapy of chemically-induced tumorigenesis are analyzed and compared with data from the literature. It has been shown that STAA have both tumor-preventive and tumor-suppressive effects on chemically-induced cancers of the colon, skin and mammary glands in rats and mice. These effects were shown to be connected with activation of the host's immune system, especially that which is responsible for the activity of T and B lymphocytes. These findings have led to a wave of new trials involving cancer immunotherapy. Understanding the mechanisms of antitumor immunity and identifying relevant tumor-specific antigens is expected to improve vaccine strategies and provide for a successful cancer therapy in the future.

This study attempted to elucidate whether the soluble tumour-associated proteins (TAA) of 66 kDa and 51 kDa molecular weight could suppress chemically induced mammary tumorigenesis. An intragastric dose of dimethylbenzanthracene (DMBA) was administered to rats and some were simultaneously immunised with the TAA. A single dose of DMBA resulted in 38% of the rats developing mammary tumours. However, simultaneous vaccination with the TAA preparation was significantly tumour-suppressive: mortality declined from 50% to 0% (p < 0.05); survival was extended from 9.4 weeks to 13.0 (p < 0.05), and 83% of the animals remained tumour free, compared to 13% of the control animals (p < 0.05). In 33% of the immunised animals the malignant tumours regressed completely. Such vaccination was also effective, although to a lesser extent, when the carcinogen dose was doubled. Then, 33% of the immunised and 22% of the control animals remained tumour-free, the latent period of malignant transformation was extended from 10.0 to 11.7 weeks, the initial tumour-free period lasted 9.3 weeks instead of 8.3 weeks and 10% survived compared to 50% of the controls. Vaccination with the soluble low molecular-weight TAA had distinct tumour-suppressive effects on mammary gland tumorigenesis.