Reduced tamoxifen accumulation is not associated with stimulated growth in tamoxifen resistance

To study tamoxifen resistance-stimulated growth, 30 female ovariectomized nude mice were implanted with tamoxifen-resistant tumors and treated with 10–1000 g/day of tamoxifen citrate subcutaneously. Tamoxifen stimulated MCF-7 tumor growth in a dose-dependent manner, with tumoral tamoxifen concentrations increasing proportionally to the dose (1–13 nmol/g), as measured by high-performance liquid chromatography (HPLC). Flow-cytometric analysis revealed that tamoxifen-resistant tumors had a different DNA content as compared with wild-type MCF-7 cells. In contrast to earlier results, these data suggest that tamoxifen resistance-stimulated growth is associated with increasing rather than decreasing tumoral tamoxifen concentrations. Furthermore, the observed ploidy changes in the tamoxifen-resistant tumors imply that a genetic basis may exist for the development of tamoxifen resistance.     

The tamoxifen dilemma.

The anti-oestrogen tamoxifen is widely used for adjuvant therapy in the treatment of women with breast cancer and has a low incidence of serious side-effects. It could also play a role as a breast cancer chemopreventive agent. However, epidemiological studies in both tamoxifen-treated breast cancer patients and in healthy women have shown that treatment results in a small increase in the incidence of endometrial cancers. While the use of tamoxifen in breast cancer patients is clearly justified, the situation for its use as a chemopreventive agent in healthy women is not so clear cut. Reasons for caution come from studies in rats that show that tamoxifen is a genotoxic mutagenic liver carcinogen. Initiation of tumours in the rat is the result of metabolic activation of tamoxifen by CYP enzymes to an electrophile(s) that binds irreversibly to DNA. This is not related to the oestrogen receptor status of the tissue. The extent of DNA damage, detected by 32P-post-labelling or accelerator mass spectrometry, is dependent both on the dose and the length of exposure. Studies have been carried out to see if such binding occurs in the uterine endometrium from tamoxifen-treated women. Results are presently inconclusive, but if such irreversible DNA binding occurs, it is at very low levels. Based on a mechanistic understanding of tamoxifen-induced liver carcinogenesis in the rat, it seems that in humans hepatic DNA damage will be close to the limit of detection by 32P-post-labelling and liver cancer will not be a significant carcinogenic risk. We cannot be certain of the mode of action of tamoxifen that results in the increase in endometrial cancers in treated women but it seems unlikely that this will be associated with a classical genotoxic mechanism.     

Sequential alpha-interferon and tamoxifen

Tamoxifen and alpha-interferon have interesting and complementary biologic effects which may be relevant for breast cancer growth and regression. The hormone responsive cell line MCF-7 was used as a model to study the biologic effects of sequential administration of these two agents. Interferon had a significant antiproliferative effect and increased ER and TGF-beta expression. The combination had at least additive antiproliferative effects as well as effects on expression of ER, TGF-beta, c-erbB-2, P24 and Ki67. alpha-IFN modulates TMX induced biologic effects and the sequential administration of alpha-IFN and TMX may lead to potentially important modulation of biologic endpoints. Further studies are appropriate.     

Pathways to tamoxifen resistance

Therapies that target the synthesis of estrogen or the function of estrogen receptor(s) have been developed to treat breast cancer. While these approaches have proven to be beneficial to a large number of patients, both de novo and acquired resistance to these drugs is a significant problem. Recent advances in our understanding of the molecular mechanisms that contribute to resistance have provided a means to begin to predict patient responses to these drugs and develop rational approaches for combining therapeutic agents to circumvent or desensitize the resistant phenotype. Here, we review common mechanisms of antiestrogen resistance and discuss the implications for prediction of response and design of effective combinatorial treatments.     

Gynaecologic effects of tamoxifen

Tamoxifen, an estrogen antagonist, is widely used as adjuvant therapy in patients with breast cancer. Its efficacy in increasing survival and reducing recurrence rates has been demonstrated in several European and American studies. However, its effects appear to be tissue specific. Tamoxifen exerts an estrogen effect (agonist) on the endometrium, myometrium and vagina. An increase in uterine cancer has been confirmed in several placebo-controlled clinical trials. Due to the widespread use of this drug, it is timely to review the gynecologic effects of tamoxifen.     

Effects of tamoxifen and octreotide LAR on the IGF-system compared with tamoxifen monotherapy

The insulin-like growth factor (IGF)-system was evaluated in 150 breast cancer patients participating in a randomised phase III trial comparing octreotide pamoate and tamoxifen with tamoxifen+placebo. Alterations in the IGF-system in the two treatment arms and individual changes with respect to outcome were compared. Serum IGF-I and -II, free IGF-I, and insulin-like growth factor binding protein 1-3 (IGFBP1-3) were measured by radioimmmunoassay (RIA)/immunoradiometric assay (IRMA) and IGFBPs by Western ligand blots (WLB) before and during treatment. Combined treatment caused a higher increase in IGFBP-1 and larger suppression of total and free IGF-I, IGF-II, and IGFBP-3 (P<0.01 for all), but less suppression of IGFBP-2 (P<0.05) compared with tamoxifen monotherapy. An increase in IGFBP-2 25% was associated with decreased progression-free survival (PFS) in the total patient population and combined treatment group. Similar response rates and time to progression in the treatment arms suggests moderate suppression of circulating IGF-I has no influence on clinical outcome.     

Serum cholesterol reduction with tamoxifen

Summary The serum cholesterol levels of 123 consecutively and newly diagnosed women with Stage I and II breast cancer taking tamoxifen were compared with a control group of 81 consecutively newly diagnosed women with Stage I and II breast cancer who were not taking a hormonal treatment or supplement. Other factors that were evaluated were age, menopausal status, tumor size, weight, height, Quetelet index, and smoking and alcohol intake history.The mean cholesterol change in patients on tamoxifen (34.2 ± 3.6 mg/dl) was significantly greater than controls (1.0 ± 4.1 mg/dl) (P<0.001). Serum cholesterol fell by more than 10 mg/dl in 72.9% of women on tamoxifen vs. 35.1% of controls and by more than 40 mg/dl in 39.9% of women on tamoxifen vs. 12.6% of controls. Multivariate analysis revealed that tamoxifen administration (P<0.0001), initial cholesterol level (P = 0.001), and age (P = 0.04) were significant factors in producing a decrease in serum cholesterol.The administration of tamoxifen as adjuvant therapy to women with newly diagnosed breast cancer resulted in a significant fall in serum cholesterol. This effect of tamoxifen on the serum cholesterol may prove to be an additional benefit in the form of reduced cardiovascular risk in these women.     

Radiation recall--another call with tamoxifen

Tamoxifen, a nonsteroidal antioestrogen, has been used as an adjuvant therapy in patients with oestrogen-receptor positive breast cancer for more than 10 years. Few cutaneous adverse side-effects of the skin are found with this therapy. In this study we present 20 cases of adverse skin effects in relation to tamoxifen during 1979-1997 reported to the Swedish Adverse Drug Reaction Register and 1160 skin side-effects reported to the World Health Organisation's International Collaborative Programme on Drug Monitoring. One new case report of radiation recall in conjunction to tamoxifen, with no sign of reactivation despite 18 months treatment with the tamoxifen analogue toremifene is also discussed in detail. This case illustrates that toremifene can be used as a second-line therapy in patients who have received radiation recall, on tamoxifen.     

Acute leukaemia during tamoxifen therapy

Tamoxifen treatment is a proven therapy for breast cancer that produces a survival advantage when used as an adjuvant, and reduces the incidence of recurrences and controlateral tumor evolution. Although this therapy has a very low toxicity profile, an increase in secondary cancers has been reported. Tamoxifen is suggested to be carinogenic both through direct genotoxic and epigenetic mechanisms. It is activated by cytochrome P450 to form reactive metabolites that bind covalently to DNA to create adducts. We report two cases that developed acute myeloid leukaemia (AML) during tamoxifen therapy for breast cancer.     

Severe lipemia induced by tamoxifen

A 61-year-old woman was treated with tamoxifen for breast cancer and had marked hyperlipoproteinemia: high plasma triglyceride levels (2790 mg/dl); increased very low density lipoprotein (VLDL) cholesterol levels (241 mg/dl); and high VLDL apoprotein B levels (126 mg/dl). Low density lipoprotein (LDL) cholesterol was decreased (104 mg/dl) and LDL apoprotein B was at 107 mg/dl. A low activity of both postheparin plasma lipoprotein lipase (LPL) and hepatic triglyceride lipase (h-TGL) was also noted. All these observations were reversed following tamoxifen withdrawal. Plasma triglyceride levels fell to 361 mg/dl. VLDL cholesterol and VLDL apoprotein B decreased to 41 mg/dl (83%) and 21 mg/dl (83%), respectively. Meanwhile, LDL cholesterol rose to 194 mg/dl (86%) and LDL apoprotein B increased to 138 mg/dl (29%). LPL and h-TGL activities did increase following tamoxifen withdrawal. Our observations show that, in some patients, the previously described weak hypertriglyceridemic effect of tamoxifen is amplified. That observation supports the concept and helps to explain that, in such severe induced lipemia, reduction of the activities of LPL and h-TGL might impede the conversion of VLDL to LDL, thus causing an amplification of the effect.     

Distribution of 4-hydroxy-N-desmethyltamoxifen and other tamoxifen metabolites in human biological fluids during tamoxifen treatment

Several metabolites of tamoxifen, including 4-hydroxy-N-desmethyltamoxifen (metabolite BX), 4-hydroxytamoxifen (metabolite B), N-desmethyltamoxifen (metabolite X), the primary alcohol (metabolite Y), and N-desdimethyltamoxifen (metabolite Z) were identified and their concentrations determined in fluids and feces from patients receiving chronic tamoxifen treatment. The biological samples investigated were serum, pleural, pericardial and peritoneal effusions, cerebrospinal fluid, saliva, bile, feces, and urine. In serum, tamoxifen itself, and the metabolites X and Z were the prevailing species, but significant amounts of the metabolites Y, B, and BX were also detected. About 3 h after drug intake tamoxifen as well as Y, B, BX, X, and Z showed a peak in serum. This may be explained by efficient metabolism of the metabolite precursor before being distributed to peripheral compartments. Upon drug withdrawal all metabolites showed first-order elimination curves which paralleled that of tamoxifen suggesting that their rate of elimination exceeded that of tamoxifen and that the serum levels are production rate limited. The protein binding of tamoxifen and its major serum metabolites (Y, X, Z) was determined and found to be higher than 98%. Albumin was the predominant carrier for tamoxifen in human plasma. The concentrations of tamoxifen and its metabolites in pleural, pericardial, and peritoneal effusions equalled those detected in serum, corresponding to an effusion/serum ratio between 0.2 and 1. Only trace amounts of tamoxifen and metabolite X were detected in cerebrospinal fluid (CSF/serum ratio less than 0.02). In saliva, concentrations of tamoxifen and X exceeded the amounts of free drug in serum, suggesting active transport or trapping of these compounds in the salivary gland. Bile and urine were rich in the hydroxylated, conjugated metabolites (Y, B, and BX), whereas in feces unconjugated metabolite B and tamoxifen were the predominating species.     

A randomised trial of tamoxifen versus tamoxifen with aminoglutethimide in post-menopausal women with advanced breast cancer

Summary Sixty-six post-menopausal women with metastatic breast cancer were randomised to receive tamoxifen or tamoxifen with aminoglutethimide. The women in the tamoxifen group were virtually free of toxicity, whilst 45% of patients in the aminoglutethimide group had toxicity and 13% discontinued the drug because of this. Responses were seen in 19% of patients receiving tamoxifen alone and 23% of those receiving both drugs. There is no indication that the increased toxicity seen with the addition of aminoglutethimide to tamoxifen in this situation is justified by an increased response rate.     

Physician recommendations regarding tamoxifen and patient utilization of tamoxifen after surgery for ductal carcinoma in situ

BACKGROUND: To date, the impact of the National Surgical Adjuvant Breast and Bowel Project (NSABP) B-24 trial reported in 1999 on the use of tamoxifen after surgery for ductal carcinoma in situ (DCIS) is unknown. The current study was designed to evaluate the impact of NSABP B-24 on current practices at a comprehensive cancer center. METHODS: The records of 350 consecutive patients with DCIS who were treated at the authors' institution between July 1999 and June 2002 were obtained from a prospective database and analyzed. Whether patients were offered tamoxifen, whether patients accepted tamoxifen, and the associated reasons were recorded along with tamoxifen-related side effects and patient compliance with therapy. Clinical and pathologic factors were evaluated for their impact on recommendations regarding tamoxifen. Differences were assessed by chi-square analysis. RESULTS: Of the 350 patients, 73 were excluded because of evidence of invasive carcinoma on final pathology review. Of the remaining 277 patients, 166 patients (60%) were offered tamoxifen, and 90 patients (54%) chose to take tamoxifen. Of 111 patients who were not offered tamoxifen, 39 patients (35%) had documented explanations, which included bilateral mastectomy (n = 25 patients), medical reasons (n = 10 patients), and already received tamoxifen for other reasons at the time of diagnosis (n = 4 patients). Of 94 patients who received tamoxifen, 20 patients (21%) discontinued use because of side effects or complications. Tamoxifen was more likely to be recommended for women who underwent segmental resection compared with women who underwent total mastectomy (P = 0.002) and for women with smaller pathologic DCIS tumors (P = 0.001). In addition, these two factors were interrelated. CONCLUSIONS: Physicians and patients remain cautious regarding the use of tamoxifen after local treatment for DCIS. The current findings have implications for current trials evaluating aromatase inhibitors and other chemopreventive agents for this disease.