Lasofoxifene versus fulvestrant for ER+/HER2- metastatic breast cancer with an ESR1 mutation: results from the randomized, phase II ELAINE 1 trial.

BACKGROUND: Acquired estrogen receptor alpha (ER/ESR1) mutations commonly cause endocrine resistance in ER+ metastatic breast cancer (mBC). Lasofoxifene, a novel selective ER modulator, stabilizes an antagonist conformation of wild-type and ESR1-mutated ER-ligand binding domains, and has antitumor activity in ESR1-mutated xenografts. PATIENTS AND METHODS: In this open-label, randomized, phase II, multicenter, ELAINE 1 study (NCT03781063), we randomized women with ESR1-mutated, ER+/human epidermal growth factor receptor 2 negative (HER2-) mBC that had progressed on an aromatase inhibitor (AI) plus a cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) to oral lasofoxifene 5 mg daily or IM fulvestrant 500 mg (days 1, 15, and 29, and then every 4 weeks) until disease progression/toxicity. The primary endpoint was progression-free survival (PFS); secondary endpoints were safety/tolerability. RESULTS: A total of 103 patients received lasofoxifene (n = 52) or fulvestrant (n = 51). The most current efficacy analysis showed that lasofoxifene did not significantly prolong median PFS compared with fulvestrant: 24.2 weeks (∼5.6 months) versus 16.2 weeks (∼3.7 months; P = 0.138); hazard ratio 0.699 (95% confidence interval 0.434-1.125). However, PFS and other clinical endpoints numerically favored lasofoxifene: clinical benefit rate (36.5% versus 21.6%; P = 0.117), objective response rate [13.2% (including a complete response in one lasofoxifene-treated patient) versus 2.9%; P = 0.124], and 6-month (53.4% versus 37.9%) and 12-month (30.7% versus 14.1%) PFS rates. Most common treatment-emergent adverse events with lasofoxifene were nausea, fatigue, arthralgia, and hot flushes. One death occurred in the fulvestrant arm. Circulating tumor DNA ESR1 mutant allele fraction (MAF) decreased from baseline to week 8 in 82.9% of evaluable lasofoxifene-treated versus 61.5% of fulvestrant-treated patients. CONCLUSIONS: Lasofoxifene demonstrated encouraging antitumor activity versus fulvestrant and was well tolerated in patients with ESR1-mutated, endocrine-resistant mBC following progression on AI plus CDK4/6i. Consistent with target engagement, lasofoxifene reduced ESR1 MAF, and to a greater extent than fulvestrant. Lasofoxifene may be a promising targeted treatment for patients with ESR1-mutated mBC and warrants further investigation.

U.S. prevalence of endocrine therapy-naïve locally advanced or metastatic breast cancer.

Background: Variations in treatment choice, or late stage at first diagnosis, mean that, despite guideline recommendations, not all patients with hormone receptor (hr)-positive locally advanced or metastatic breast cancer (la/mbca) will have received endocrine therapy before disease progression. In the present study, we aimed to estimate the proportion of women with postmenopausal hr-positive la/mbca in the United States who are endocrine therapy-naïve. Methods: Women in the Optum Electronic Health Record (ehr) database with a breast cancer (bca) diagnosis (January 2008-March 2015) were included. Patient and malignancy characteristics were identified using structured data fields and natural-language processing of free-text clinical notes. The proportion of women with postmenopausal hr-positive, human epidermal growth factor 2 (her2)-negative (or unknown) la/mbca who had not received prior endocrine therapy was determined. Results were extrapolated to the entire U.S. population using the U.S. National Cancer Institute's Surveillance, Epidemiology, and End Results database. Results are presented descriptively. Results: In the ehr database, 11,831 women with bca had discernible information on postmenopausal status, hr status, and disease stage. Of those women, 1923 (16.3%) had postmenopausal hr-positive, her2-negative (or unknown) la/mbca, and 70.7% of those 1923 patients (n = 1360) had not received prior endocrine therapy, accounting for 11.5% of the overall population. Extrapolating those estimates nationally suggests an annual incidence of 14,784 cases, and a 5-year limited duration prevalence of 50,638 cases. Conclusions: A substantial proportion of women with postmenopausal hr-positive la/mbca in the United States could be endocrine therapy-naïve.

A pilot study of cabergoline for the treatment of metastatic breast cancer.

PURPOSE: The prolactin (PRL) receptor is over-expressed in breast cancer, and pre-clinical data indicate that it contributes to breast oncogenesis. Cabergoline is a potent dopamine receptor agonist of D2 receptors and has a direct inhibitory effect on pituitary PRL secretion. METHODS: A phase II study of cabergoline in patients with metastatic breast cancer was conducted. The primary end point of the study was to determine the clinical benefit rate (CBR) at 2 months. Eligible patients had tumors of any receptor status with no limit of prior lines of therapy. Measurable and unmeasurable diseases were allowed. Cabergoline 1 mg orally, twice weekly (1 cycle = 4 weeks) was given until disease progression or unacceptable toxicity. PRL receptor immunohistochemical staining was performed on available baseline tumor tissue; serial serum PRL levels were assessed. RESULTS: Twenty women were enrolled; 18 were evaluable for CBR. Tumor receptor status was distributed as follows: HR-any/HER2+ 2(10%), HR+/HER2- 18 (90%). The CBR was 33% (6/18), median progression free survival was 1.8 months, and median overall survival was 10.4 months. Two patients experienced disease control for over 12 months. Most common treatment-related adverse events were nausea (30%), fatigue (25%), and elevation in alkaline phosphatase (15%). Nine patients had baseline tissue for analysis; there was no association between baseline tumor PRL receptor expression and clinical benefit (p = 0.24). Change in serum PRL level and response were not correlated after 2 months of treatment (p = 0.64). CONCLUSION: Cabergoline was well tolerated, and while the ORR was low, a small subset of patients experienced extended disease control.

Meta-analysis of selected toxicity endpoints of CDK4/6 inhibitors: Palbociclib and ribociclib.

PURPOSE: Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors such as palbociclib and ribociclib are associated with distinct adverse effects (AEs) compared to other targeted therapies. This meta-analysis of clinical trials summarizes these agents' toxicity profile. METHODS: A librarian-guided literature search was conducted in March of 2017. The trials needed to have at least one of the study arms consisting of palbociclib or ribociclib monotherapy at currently FDA approved dose regimens. Heterogeneity across studies was analyzed using I2 statistics. Data were analyzed using random effects meta-analysis for absolute risks. RESULTS: Seven randomized trials and 1,332 patients were included in our meta-analysis. There was evidence of significant heterogeneity between studies for serious AEs but not for death. The pooled absolute risk (AR) for all-causality serious AEs and treatment-related death were 16% and 0%, respectively. Patients treated with CDK 4/6 inhibitors had an AR of grade 3/4 neutropenia of 61%; neutropenic fever and infections were rare (1% and 3%, respectively). Grade 3/4 nausea, vomiting, and rash were rare. There was no significant correlation between age of patients at study entry and the risk of grade 3/4 neutropenia. CONCLUSION: Treatment with CDK 4/6 inhibitors is well tolerated and associated with a low risk of treatment-related deaths. There is an increased AR of grade 3/4 neutropenia but a low AR of associated infections.

Systematic analysis of early phase clinical studies for patients with breast cancer: Inclusion of patients with brain metastasis.

PURPOSE: This systematic review aims to better define the limitations and patterns with which patients with MBC and CNS metastasis are enrolled into early phase developmental therapeutics trials. METHODS: In June 2016, PubMed search was conducted using the following keywords: "Breast cancer". Drug-development phase 1, phase 2 or phase 1/2 trials for patients with MBC were included. Multiple-histology trials and trials without an efficacy endpoint were excluded. RESULTS: In total, 1474 studies were included; Inclusion criteria for 423 (29%) allowed for CNS metastasis, 770 (52%) either excluded or did not document eligibility of patients with CNS disease. Trials accruing patients with HER2-positive MBC and including targeted therapies had higher odds of allowing for patients with CNS disease (adjusted OR 1.56, 95% CI 1.08-2.2.6; p=0.019 and 1.49, 95% 1.08-2.06; p=0.014, respectively). There were also higher odds of accrual of patients with CNS involvement into clinical trials over time (odds ratio=1.10, 95% CI 1.07-1.12; p<0.0001). CONCLUSION: Most published early phase clinical trials either did not clearly document or did not allow for accrual of patients with CNS disease. Early phase trials with targeted agents or enrolling HER2+ MBC had higher odds of permitting CNS metastases.

Developmental therapeutics for patients with breast cancer and central nervous system metastasis: current landscape and future perspectives.

Breast cancer is the second-leading cause of metastatic disease in the central nervous system (CNS). Recent advances in the biological understanding of breast cancer have facilitated an unprecedented increase of survival in a subset of patients presenting with metastatic breast cancer. Patients with HER2 positive (HER2+) or triple negative breast cancer are at highest risk of developing CNS metastasis, and typically experience a poor prognosis despite treatment with local and systemic therapies. Among the obstacles ahead in the realm of developmental therapeutics for breast cancer CNS metastasis is the improvement of our knowledge on its biological nuances and on the interaction of the blood­brain barrier with new compounds. This article reviews recent discoveries related to the underlying biology of breast cancer brain metastases, clinical progress to date and suggests rational approaches for investigational therapies.

Elevated incidence of fractures in women with invasive breast cancer.

UNLABELLED: This study evaluates the incidence of bone fractures in women with BC.We found that women with invasive breast cancer are at an increased risk for bone fractures, with fractures most commonly occurring at lower extremity and vertebral sites. The risk is further increased in women undergoing cancer therapy. INTRODUCTION: Bone loss and fractures in breast cancer have generally been attributed to aromatase inhibitor use. This study assessed the incidence of fractures after invasive breast cancer diagnosis and evaluated bone density and FRAX risk calculation at time of fracture occurrence. METHODS: Retrospective cohort study of women with invasive breast cancer [June 2003-December 2011] who participated in an academic hospital based genetic biobank. Demographic and clinical characteristics were abstracted from the electronic medical record (EMR). RESULTS: A total of 422 women with invasive breast cancer were assessed; 79 (28 %) sustained fractures during the observation period; fractures occurred at multiple skeletal sites in 27 cases (116 fractures). The incidence of fractures was 40 per 1000 person-years. Women who sustained fractures were mostly white and had a family history of osteoporosis (36.9 %, p = 0.03) or history of a prior fracture (6/79, p = 0.004). Fractures occurred 4.0 years (range 0-12 years) after cancer diagnosis. Fracture cases had femoral neck bone mineral density (BMD) of 0.72 + 0.12 g/cm(2), T-score of -1.2, that is, within the low bone mass range. Fractures most commonly occurred in lower extremities, vertebral, and wrist sites. Hip fractures accounted for 11 % of fractures, occurring at a median age of 61 years. CONCLUSIONS: Fractures occur shortly after commencing cancer therapy. Rapid bone loss associated with cancer therapy may precipitate fractures. Fractures occur at relatively higher BMD in BC. Occurrence of fractures in invasive breast cancer raises the possibility of cancer-induced impairment in bone quality.

ERK-regulated αB-crystallin induction by matrix detachment inhibits anoikis and promotes lung metastasis in vivo.

Evasion of extracellular matrix detachment-induced apoptosis ('anoikis') is a defining characteristic of metastatic tumor cells. The ability of metastatic carcinoma cells to survive matrix detachment and escape anoikis enables them to disseminate as viable circulating tumor cells and seed distant organs. Here we report that αB-crystallin, an antiapoptotic molecular chaperone implicated in the pathogenesis of diverse poor-prognosis solid tumors, is induced by matrix detachment and confers anoikis resistance. Specifically, we demonstrate that matrix detachment downregulates extracellular signal-regulated kinase (ERK) activity and increases αB-crystallin protein and messenger RNA (mRNA) levels. Moreover, we show that ERK inhibition in adherent cancer cells mimics matrix detachment by increasing αB-crystallin protein and mRNA levels, whereas constitutive ERK activation suppresses αB-crystallin induction during matrix detachment. These findings indicate that ERK inhibition is both necessary and sufficient for αB-crystallin induction by matrix detachment. To examine the functional consequences of αB-crystallin induction in anoikis, we stably silenced αB-crystallin in two different metastatic carcinoma cell lines. Strikingly, silencing αB-crystallin increased matrix detachment-induced caspase activation and apoptosis but did not affect cell viability of adherent cancer cells. In addition, silencing αB-crystallin in metastatic carcinoma cells reduced the number of viable circulating tumor cells and inhibited lung metastasis in two orthotopic models, but had little or no effect on primary tumor growth. Taken together, our findings point to αB-crystallin as a novel regulator of anoikis resistance that is induced by matrix detachment-mediated suppression of ERK signaling and promotes lung metastasis. Our results also suggest that αB-crystallin represents a promising molecular target for antimetastatic therapies.

Emerging approaches for treating HER2-positive metastatic breast cancer beyond trastuzumab.

Because metastatic breast cancer (MBC) is incurable in most cases, the goals of treatment are improvement in quality of life, management of symptoms, and prolonged survival. The human epidermal growth factor receptor 2 (HER2) is overexpressed in up to 30% of breast tumors, and before the development of HER-targeted therapy, HER2 positivity was predictive of poorer clinical outcomes. Trastuzumab and pertuzumab (anti-HER2 monoclonal antibodies), lapatinib (a small molecule inhibitor of HER2 and the epidermal growth factor receptor [EGFR]) are approved for treating HER2-positive MBC in the United States. Although trastuzumab plus chemotherapy is currently regarded as the first-line standard of care for HER2-positive MBC, it is not without shortcomings; these include its association with certain adverse events (e.g. cardiotoxic effect) and development of resistance. A number of investigational agents that target HER2 and other members of that receptor family are in clinical development for patients with HER2-positive MBC whose disease has progressed on trastuzumab. In addition, in an effort to overcome treatment resistance, clinical trials are evaluating combination therapy (investigational HER-targeted agents with trastuzumab or lapatinib). This review discusses recently completed and ongoing phase II and III clinical trials of investigational HER-targeted agents in the setting of trastuzumab-progressive, HER2-positive MBC.

Taxanes for the treatment of metastatic breast cancer.

Taxanes have remained a cornerstone of breast cancer treatment over the past three decades, improving the lives of patients with both early- and late-stage disease. The purpose of this review is to summarize the current role of taxanes, including an albumin-bound formulation that enhances delivery of paclitaxel to tumors, in the management of metastatic breast cancer (MBC). Since the introduction of Cremophor EL-paclitaxel to the clinic in the mid-1990s, a substantial amount of investigation has gone into subjects such as formulation, dose, schedule, and taxane resistance, allowing physicians greater flexibility in treating patients with MBC. This review will also examine how the shrinking pool of taxane-naive patients, a result of the expansion of taxanes into the neoadjuvant and adjuvant settings, will respond to taxane retreatment for metastatic disease. Taxane treatment seems likely to continue to play an important role in the treatment of MBC.

Adjuvant therapy of breast cancer.

In the past few years the treatment of early stage breast cancer has gone through several important changes. Both chemotherapy and hormonal therapy have been shown by large, randomized trials to offer a survival advantage. The most commonly used chemotherapeutic agents used in the US are doxorubicin and cyclophosphamide (AC). However, 3 studies have suggested that there may be an advantage in the use of taxanes in the adjuvant treatment of breast cancer. Furthermore the use of dose dense chemotherapy, incorporating AC and paclitaxel, has shown very promising results. It is well established that tamoxifen (T), a selective estrogen receptor modulator (SERM), improves overall survival (OS) in women with hormone receptor (HR) positive breast cancer. However, the results from large multicenter, randomized trials, suggest the potential superiority of aromatase inhibitors (AIs), compared to T or an advantage of sequencing T followed by an AI. The role ovarian suppression is still being investigated in patients who have received prior chemotherapy. Newer agents, such as the monoclonal antibody against the her2/neu receptor, trastuzumab, are now being studied as adjuvant therapy in early stage breast cancer. In the next few years, with the completion of several large randomized trials, we will be able to answer several questions, including the optimal way of incorporating AIs into the adjuvant therapy, the long-term sequella of using trastuzumab in the adjuvant treatment of breast cancer and the role of ovarian suppression combined with an AI in premenopausal women with breast cancer.

Neoadjuvant docetaxel followed by adjuvant doxorubicin and cyclophosphamide in patients with stage III breast cancer.

BACKGROUND: To evaluate clinical and pathologic response to neoadjuvant docetaxel therapy in patients with stage III breast cancer. PATIENTS AND METHODS: Forty-five patients were planned to receive four cycles of docetaxel 100 mg/m2 every 3 weeks, followed by surgery, four cycles of doxorubicin 60 mg/m2 and cyclophosphamide 600 mg/m2 (AC) every 3 weeks, radiation therapy (RT), and tamoxifen when indicated. RESULTS: After four cycles of neoadjuvant docetaxel, the clinical response rate within the breast was 59% (95% CI 42% to 73%) and overall (breast and axilla) was 49% (95% CI 38% to 72%) in the intention-to-treat (ITT) population. At the time of surgery, 10% (n=4) of patients had a pathologic complete response (pCR) in the breast, 27% (n=11) had a pCR within the axillary lymph nodes, and 7% (n=3) had a pCR in the breast and axilla (95% CI 2% to 21%). An additional 5% (n=2) had minimal residual invasive tumor (<5 mm). The 5-year overall survival rate was 80%. The percentage of patients with grade 3/4 neutropenia was similar during docetaxel (93%) and AC (86%), while a greater percentage of patients had febrile neutropenia during docetaxel treatment (27%) compared with AC treatment (7%). CONCLUSIONS: Neoadjuvant docetaxel followed by surgery, adjuvant AC, hormonal therapy where indicated, and RT is an active regimen for patients with stage III breast cancer.

Docetaxel combined with trastuzumab is an active regimen in HER-2 3+ overexpressing and fluorescent in situ hybridization-positive metastatic breast cancer: a multi-institutional phase II trial.

PURPOSE: To determine the efficacy and safety of weekly docetaxel and trastuzumab as first- or second-line therapy in women with HER-2-overexpressing metastatic breast cancer and to correlate the efficacy of trastuzumab with HER-2 status as determined by immunohistochemistry assay and fluorescent in situ hybridization (FISH). PATIENTS AND METHODS: Twenty-six women with HER-2-positive (HercepTest [Dako Corp, Carpenteria, CA]2 to 3+) metastatic breast cancer were enrolled onto this study of trastuzumab (4 mg/kg load; 2 mg/kg/wk administered intravenously) and docetaxel (35 mg/m2/wk for 6 weeks). RESULTS: Using an intent-to-treat analysis, the overall response rate was 50% (13 of 26 patients). Eight patients (31%) had a period of stable disease posttherapy. Among HER-2 3+ patients, the overall response rate was 63% (12 of 19 patients) compared with a 14% response rate (one of seven patients) for HER-2 2+ patients (P=.07). Patients with FISH-positive tumors experienced an overall response rate of 64%. Median time to progression was 12.4 months for the entire cohort (HER-2 3+ tumors, 12.3 months; HER-2 2+ lesions, 9.5 months) and median survival was 22.1 months. All HER-2 3+ patients were FISH-positive; the only HER-2 2+ patient responding to treatment was also FISH-positive. Grade 4 toxicities occurred in four patients; most toxicities were mild. CONCLUSION: Trastuzumab plus docetaxel is an active and well-tolerated regimen in women with HER-2 3+ overexpressing or FISH-positive metastatic breast cancer.

A Phase II trial of cisplatin plus WR-2721 (amifostine) for metastatic breast carcinoma: an Eastern Cooperative Oncology Group Study (E8188).

BACKGROUND: Cisplatin has minimal antitumor activity when used as second- or third-line treatment of metastatic breast carcinoma. Older reports suggest an objective response rate of 8% when 60-120 mg/m2 of cisplatin is administered every 3-4 weeks. Although a dose-response effect has been observed with cisplatin, the dose-limiting toxicities associated with cisplatin (e.g., nephrotoxicity, ototoxicity, and neurotoxicity) have limited its use as a treatment for breast carcinoma. WR-2721 or amifostine initially was developed to protect military personnel in the event of nuclear war. Amifostine subsequently was shown to protect normal tissues from the toxic effects of alkylating agents and cisplatin without decreasing the antitumor effect of the chemotherapy. Early trials of cisplatin and amifostine also suggested that the incidence and severity of cisplatin-induced nephrotoxicity, ototoxicity, and neuropathy were reduced. METHODS: A Phase II study of the combination of cisplatin plus amifostine was conducted in patients with progressive metastatic breast carcinoma who had received one, but not more than one, chemotherapy regimen for metastatic disease. Patients received amifostine, 910 mg/m2 intravenously over 15 minutes. After completion of the amifostine infusion, cisplatin 120 mg/m2 was administered over 30 minutes. Intravenous hydration and mannitol was administered before and after cisplatin. Treatment was administered every 3 weeks until disease progression. RESULTS: Forty-four patients were enrolled in the study of which 7 (16%) were ineligible. A median of 2 cycles of therapy was administered to the 37 eligible patients. Six partial responses were observed for an overall response rate of 16%. Most patients (57%) stopped treatment because of disease progression. Neurologic toxicity was reported in 52% of patients. Seven different life-threatening toxicities were observed in patients while receiving treatment. CONCLUSIONS: The combination of cisplatin and amifostine in this study resulted in an overall response rate of 16%. Neither a tumor-protective effect nor reduced toxicity to normal tissues was observed with the addition of amifostine to cisplatin in this trial.

Selective estrogen-receptor modulators in 2001.

Tamoxifen (Nolvadex), a selective estrogen-receptor modulator, or SERM, is currently the endocrine therapy of choice for all stages of hormone-responsive breast cancer. Only tamoxifen has been approved by the US Food and Drug Administration to reduce the incidence of breast cancer in high-risk women. Despite tamoxifen's antiestrogenic effects in breast tissue, it exhibits paradoxical estrogenic effects in other tissues in the body. These effects result in the maintenance of bone mineral density, but a three- to fourfold increase in endometrial cancer in postmenopausal women. Additionally, tamoxifen can result in troublesome hot flashes and serious thromboembolic events. For this reason, current research is focusing on new agents that may maintain the beneficial effects of tamoxifen while reducing its adverse effects. Raloxifene (Evista) is another SERM, approved for the prevention of osteoporosis in postmenopausal women and now being compared with tamoxifen in an ongoing breast cancer prevention trial. Like tamoxifen, raloxifene is associated with hot flashes and thromboembolic events, but its association with the risk of endometrial cancer is unknown. A number of new SERMs are in preclinical or clinical development in an attempt to improve upon the safety profile of tamoxifen. Additionally, selective aromatase inhibitors are being examined in the early breast cancer setting.

Clinical status of capecitabine in the treatment of breast cancer.

New treatment strategies for advanced breast cancer have focused on both the development of new molecular targets in breast cancer cells, as well as improving the therapeutic index of presently available therapy. The development of capecitabine (Xeloda), a new oral fluoropyrimidine, is an example of a chemotherapy drug that has single-agent activity in heavily pretreated patients with advanced breast cancer, with the added convenience of good oral bioavailability. Capecitabine is an excellent treatment option for patients who require symptom palliation and who prefer oral medications. The discussion that follows reviews the clinical data on the use of capecitabine in advanced breast cancer.

Primary (neoadjuvant) chemotherapy with docetaxel in breast cancer.

The use of primary or neoadjuvant chemotherapy for locally advanced breast cancer, including those patients with inflammatory breast cancer, is well established. The use of primary chemotherapy has also been investigated in patients with operable breast cancer. The potential benefit of using primary chemotherapy is the opportunity to administer systemic therapy at an earlier timepoint, where it may be more effective against microscopic disease. In addition, primary chemotherapy for patients with operable breast cancer may also result in higher rates of breast conservation, axillary nodal downstaging, and potential improvement in patient outcome. A variety of different chemotherapy drugs have been evaluated in the primary chemotherapy setting. One of the most common approaches is to use an anthracycline-based regimen for 4 or more cycles of treatment before considering definitive local therapy. Although high tumor response rates have been reported using anthracycline-based regimens, the fraction of patients actually attaining a pathologic complete response has remained small (less than 20%). With the introduction of new chemotherapy drugs, such as docetaxel, which is associated with a very high tumor response rate in metastatic disease, a natural evolution of clinical investigation is to use docetaxel in the neoadjuvant or primary chemotherapy setting. Some of the recent trials that have evaluated single-agent docetaxel, docetaxel-based chemotherapy combinations, and novel sequencing strategies that include docetaxel in the neoadjuvant setting are reviewed. The results from these trials clearly suggest that docetaxel-containing treatment strategies can be considered a standard in the primary chemotherapy setting

A pilot trial of suramin in metastatic breast cancer to assess antiangiogenic activity in individual patients.

Suramin is a polysulfonated naphthylurea with multiple potential mechanisms of action against tumors, including the ability to bind growth factors known to promote tumor angiogenesis. Using an established fixed dosing scheme for the administration of suramin in patients, a pilot study was conducted in patients with progressive, metastatic breast cancer. The primary objective of this trial is to define the effect of suramin on the angiogenic activity in individual patients using in vitro laboratory assays. The secondary objective was to assess the antitumor effect of suramin in a population of metastatic breast cancer patients. No objective tumor responses were observed in any of the 9 patients who received treatment with suramin, however 1 patient did maintain stable disease status. The strength of angiogenic activity present in patient samples was assessed by testing patient plasma in the capillary endothelial cell migration assay. Angiogenic activity followed over time was lowest in patients with the highest suramin concentrations and highest in patients with the lowest suramin concentrations. We conclude that it is feasible to continually monitor the activity of antiangiogenic agents in individual patients without relying on clinical tumor response.