Paclitaxel-carboplatin combination chemotherapy in advanced breast cancer: accumulating evidence for synergy, efficacy, and safety

Paclitaxel and Carboplatin in Combination with Low-intensity Pulsed Ultrasound for Glioblastoma

PURPOSE

We recently reported on clinical trials for patients with recurrent glioblastoma where low-intensity pulsed ultrasound and microbubbles (LIPU/MB) improved paclitaxel or carboplatin delivery into the brain. Here, we report variable local tumor control with paclitaxel at the maximal/target dose in our phase I trial (NCT04528680). To address this, we investigated the combination of paclitaxel with carboplatin in preclinical glioma models.

EXPERIMENTAL DESIGN

We performed MRI-based analysis to evaluate disease control in patients from our trial. We studied the cytotoxicity of paclitaxel and carboplatin against 11 human glioma lines as monotherapy and in combination at concentrations derived from human intraoperative studies. Synergy was assessed with the Loewe model and the survival benefit evaluated in two xenografts. We examined the effects on cell cycle progression, DNA damage, and apoptosis.

RESULTS

Patients treated with paclitaxel and LIPU/MB exhibited variable local tumor control, which correlated with overall survival. We observed limited cross-resistance to paclitaxel and carboplatin in glioma lines, with almost a third of them being exclusively susceptible to one drug. This combination led to susceptibility of 81% of lines and synergy in 55% of them. The combination proved more efficacious in two intracranial xenografts when administered with LIPU/MB, leading to complementary effects on cell cycle arrest.

CONCLUSIONS

Combining paclitaxel and carboplatin in gliomas may be more efficacious than monotherapy, as in other cancers, due to synergy and independent susceptibility to each drug. These results form the basis for an ongoing phase II trial (NCT04528680) where we investigate this combination with LIPU/MB.

Combination chemotherapy in rodents: a model for chemotherapy-induced neuropathic pain and pharmacological screening

Chemotherapy-induced neuropathic pain (CINP) remains a therapeutic challenge, with no US-FDA approved drugs or effective treatments available. Despite significant progress in unravelling the pathophysiology of CINP, the clinical translation of this knowledge into tangible outcome remains elusive. Here, we employed behavioural and pharmacological approaches to establish and validate a novel combination-based chemotherapeutic model of peripheral neuropathy. Male Sprague Dawley rats were subjected to chemotherapy administration followed by assessment of pain behaviour at different time-points post-chemotherapy. Paclitaxel-treated animals displayed an enhanced thermal and mechanical hypersensitivity from day four onwards which continued till day thirty-five post last paclitaxel injection. Notably, rats subjected to combination chemotherapy, displayed prolonged hypersensitivity that emerged on day four and persisted until day fifty-six. RT-PCR analysis revealed significant upregulation in DRG and spinal mRNA expressions of TRP channels (TRPA1, TRPV1, & TRPM8), pro-inflammatory cytokines (TNF-α & IL-1β) and neuropeptides, Substance P and CGRP in both the pain models. Interestingly, the combination chemotherapy model demonstrated a significant increase in DRG and spinal NR2B expressions compared to rats solely treated with paclitaxel. Pharmacological investigations revealed that gabapentin treatment substantially mitigates pain hypersensitivity in both the combined chemotherapy and paclitaxel-administered groups, with the simultaneous reversal of cellular and molecular changes observed in the lumbar DRG and spinal cord of rats. The findings from this study suggests that combination chemotherapy model exhibits heightened and prolonged hypersensitivity in comparison to the conventional paclitaxel-induced neuropathic pain model. This model not only recapitulates clinical biomarkers of neuropathy but also presents a potential alternative platform for screening analgesic drugs targeted at CINP.

Paclitaxel inhibits hepatocellular carcinoma tumorigenesis by regulating the circ_0005785/miR-640/GSK3β

Paclitaxel (PTX) is an effective chemotherapeutic agent for cancer patients. It has been reported that circular RNA (circRNA) circ_0005785is involved in the progression of hepatocellular carcinoma (HCC). The purpose of this study is to explore the role and mechanism of circ_0005785 in the PTX resistance of HCC. Cell viability, proliferation, invasion, migration, apoptosis, and angiogenesis were detected using 3-(4, 5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2-H-tetrazolium bromide (MTT), colony formation, transwell, wound-healing, flow cytometry, and tube formation assay. Circ_0005785, microRNA-640 (miR-640), and Glycogen synthase kinase-3 beta (GSK3β) levels were detected using real-time quantitative polymerase chain reaction. Protein levels of Proliferating cell nuclear antigen (PCNA), Bcl-2, and GSK3β were measured using western blot assay. After being predicted using Circular RNA interactome or TargetScan, binding between miR-640 and circ_0005785 or GSK3β was verified using dual-luciferase reporter and RNA Immunoprecipitation assay. PTX treatment could repress HCC cell viability, decrease circ_0005785 and GSK3β expression, and increase the miR-640 level in HCC cell lines. Furthermore, circ_0005785 and GSK3β were increased, and miR-640 was decreased in HCC tissues and cell lines. Moreover, circ_0005785 knockdown hindered proliferation, migration, invasion, angiogenesis, and boosted apoptosis in PTX-treated HCC cells in vitro. In addition, circ_0005785 silencing improved the PTX sensitivity of HCC in vivo. Mechanistically, circ_0005785 acted as a sponge of miR-640 to regulate GSK3β expression. PTX restrained HCC tumorigenesis partly via regulating the circ_0005785/miR-640/GSK3β axis, hinting at a promising therapeutic target for the HCC treatment.

Preclinical tolerance evaluation of the addition of a cisplatin-based dry powder for inhalation to the conventional carboplatin-paclitaxel doublet for treatment of non-small cell lung cancer

Despite the advances in targeted therapies and immunotherapy for non-small cell lung cancer (NSCLC) patients, the intravenous administration of carboplatin (CARB) and paclitaxel (PTX) in well-spaced cycles is widely indicated for the treatment of NSCLC from stage II to stage IV. Our strategy was to add a controlled-release cisplatin-based dry-powder for inhalation (CIS-DPI-ET) to the conventional CARB-PTX-IV doublet, administered during the treatment off-cycles to intensify the therapeutic response while avoiding the impairment of pulmonary, renal and haematological tolerance of these combinations. The co-administration of CIS-DPI-ET (0.5 mg/kg) and CARB-PTX-IV (17-10 mg/kg) the same day showed a higher proportion of neutrophils in BALF (35 ± 7% vs 1.3 ± 0.8%), with earlier regenerative anaemia than with CARB-PTX-IV alone. A first strategy of CARB-PTX-IV dose reduction by 25% also induced neutrophil recruitment, but in a lower proportion than with the first combination (20 ± 6% vs 0.3 ± 0.3%) and avoiding regenerative anaemia. A second strategy of delaying CIS-DPI-ET and CARB-PTX-IV administrations by 24 h avoided both the recruitment of neutrophils in BALF and regenerative anaemia. Moreover, all these groups showed higher cytotoxicity (LDH activity, protein content) with no higher renal toxicities. These two strategies seem interesting to be assessed in terms of antitumor efficacy in mice.

Preferential uptake of antibody targeted calcium phosphosilicate nanoparticles by metastatic triple negative breast cancer cells in co-cultures of human metastatic breast cancer cells plus bone osteoblasts

Calcium phosphosilicate nanoparticles (CPSNPs) are bioresorbable nanoparticles that can be bioconjugated with targeting molecules and encapsulate active agents and deliver them to tumor cells without causing damage to adjacent healthy tissue. Data obtained in this study demonstrated that an anti-CD71 antibody on CPSNPs targets these nanoparticles and enhances their internalization by triple negative breast cancer cells in-vitro. Caspase 3,7 activation, DNA damage, and fluorescent microscopy confirmed the apoptotic breast cancer response caused by targeted anti-CD71-CPSNPs encapsulated with gemcitabine monophosphate, the active metabolite of the chemotherapeutic gemcitabine used to treat cancers including breast and ovarian. Targeted anti-CD71-CPSNPs encapsulated with the fluorophore, Rhodamine WT, were preferentially internalized by breast cancer cells in co-cultures with osteoblasts. While osteoblasts partially internalized anti-CD71-GemMP-CPSNPs, their cell growth was not affected. These results suggest that CPSNPs may be used as imaging tools and selective drug delivery systems for breast cancer that has metastasized to bone.

Targeted Inhibition of miR-221/222 Promotes Cell Sensitivity to Cisplatin in Triple-Negative Breast Cancer MDA-MB-231 Cells

Cisplatin has been widely used in the treatment of a various types of cancers including triple-negative breast cancer (TNBC) by damaging DNA and inducing apoptosis. However, its anti-cancer effects are often limited due to chemo-resistance, which is one of the main reasons causing cancer relapse and metastasis. To overcome resistance, cisplatin is often used in combination with other drugs or molecules. Our study found that the targeted inhibition of miR-221/222 in MDA-MB-231 cells promoted cisplatin-induced cell apoptosis, and increased the cell sensitivity to cisplatin in vitro. Much higher expression levels of miR-221/222 were detected in the cisplatin-resistant MDA-MB-231 cells and in cisplatin-resistant breast cancer patients. The combination chemotherapy of cisplatin with anti-miR-221/222 showed much higher efficiency in suppressing tumor growth in the mice transplanted with MDA-MB-231 cells. In addition, anti-miR-221 and anti-miR-222 showed synergetic effects on improving sensitivity to cisplatin in MDA-MB-231 cells. Suppression of SOCS1-STAT3-Bcl-2 pathway and activation of p53-Pten signaling both contribute to anti-miR-221/222-induced sensitivity to cisplatin in MDA-MB-231 cells. These findings suggest the potential of a novel approach for the combination chemotherapy of cisplatin with small non-coding RNA in treatment of human TNBC.

Metastatic and triple-negative breast cancer: challenges and treatment options

The major current conventional types of metastatic breast cancer (MBC) treatments include surgery, radiation, hormonal therapy, chemotherapy, or immunotherapy. Introducing biological drugs, targeted treatment and gene therapy can potentially reduce the mortality and improve the quality of life in patients with MBC. However, combination of several types of treatment is usually recommended. Triple negative breast cancer (TNBC) accounts for 10-20% of all cases of breast carcinoma and is characterized by the low expression of progesterone receptor (PR), estrogen receptor (ER), and human epidermal growth factor receptor 2 (HER2). Consequently, convenient treatments used for MBC that target these receptors are not effective for TNBC which therefore requires special treatment approaches. This review discusses the occurrence of MBC, the prognosis and predictive biomarkers of MBC, and focuses on the novel advanced tactics for treatment of MBC and TNBC. Nanotechnology-based combinatorial approach for the suppression of EGFR by siRNA and gifitinib is described.

Antitumor activity and safety profile of weekly carboplatin plus paclitaxel in metastatic breast cancer: a ten-year, monocentric, retrospective study

BACKGROUND

Taxanes are a mainstay in the treatment of metastatic breast cancer (mBC). Combination chemotherapy, including platinum-taxens doublets, can improve tumor responses and progression-free survival (PFS), but is associated with more toxicities and an uncertain benefit in terms of overall survival (OS).

METHODS

We performed a retrospective study on 274 consecutive patients with mBC treated at the Division of Medical Oncology of Fondazione IRCCS Istituto Nazionale Tumori, Milan, Italy, during the decade 2007-2016 with the combination of carboplatin AUC 2 plus paclitaxel 80 mg/m², both given on days 1 and 8 in every 21-day cycle.

RESULTS

264 patients were evaluable for treatment safety and activity. The objective response rate (ORR) was 44.7%. Median PFS and OS were 8.6 and 23.7 months, respectively. Triple-negative breast cancer (TNBC) patients had significantly lower PFS and OS times compared to other biology groups. At multivariable analysis, previous exposure to taxanes, HR-positive HER2-negative biology, a higher number of metastatic sites, and de novo metastatic disease at diagnosis were associated with reduced PFS, while receiving maintenance therapy correlated with improved PFS. Overall, the treatment was quite well tolerated, with 10.2% of patients discontinuing one or both drugs because of adverse events (AEs). G3-G4 neutropenia occurred in 16.8% of patients, while the incidence of febrile neutropenia was 2.3%.

CONCLUSIONS

Weekly carboplatin-paclitaxel regimen is active and well tolerated in mBC treatment. Prospective studies should be conducted to compare its efficacy and tolerability with standard single-agent paclitaxel or docetaxel treatment schedules, as well as with more recent combination regimens.

Mammalian target of rapamycin inhibitor RAD001 sensitizes endometrial cancer cells to paclitaxel-induced apoptosis via the induction of autophagy

The aim of the present study was to investigate the effects of the mammalian target of rapamycin (mTOR) inhibitor, RAD001, on the growth of human endometrial cancer cells. The effects of RAD001 on human endometrial cancer Ishikawa and HEC-1A cell proliferation were determined by MTT assay. Green fluorescent protein microtubule-associated protein 1 light chain 3α (GFP-LC3) protein aggregates were observed under a confocal microscope, and Ishikawa and HEC-1A cell apoptosis was detected using flow cytometry. The expression levels of LC3-I, LC3-II and mTOR proteins were detected by western blot analysis. The results showed that RAD001 effectively inhibited human endometrial cancer Ishikawa and HEC-1A cell proliferation via downregulation of AKT/mTOR phosphorylation. Moreover, RAD001 induced autophagic cell death and a higher sensitivity to paclitaxel-induced apoptosis. These results indicate that RAD001 could have therapeutic potential in human endometrial cancer with hyperactivated AKT/mTOR signaling.

A nomogram for predicting pathological complete response in patients with human epidermal growth factor receptor 2 negative breast cancer

Background

The response to neoadjuvant chemotherapy has been proven to predict long-term clinical benefits for patients. Our research is to construct a nomogram to predict pathological complete response of human epidermal growth factor receptor 2 negative breast cancer patients.

Methods

We enrolled 815 patients who received neoadjuvant chemotherapy from 2003 to 2015 and divided them into a training set and a validation set. Univariate logistic regression was performed to screen for predictors and construct the nomogram; multivariate logistic regression was performed to identify independent predictors.

Results

After performing the univariate logistic regression analysis in the training set, tumor size, hormone receptor status, regimens of neoadjuvant chemotherapy and cycles of neoadjuvant chemotherapy were the final predictors for the construction of the nomogram. The multivariate logistic regression analysis demonstrated that T4 status, hormone receptor status and receiving regimen of paclitaxel and carboplatin were independent predictors of pathological complete response. The area under the receiver operating characteristic curve of the training set and the validation set was 0.779 and 0.701, respectively.

Conclusions

We constructed and validated a nomogram to predict pathological complete response in human epidermal growth factor receptor 2 negative breast cancer patients. We also identified tumor size, hormone receptor status and paclitaxel and carboplatin regimen as independent predictors of pathological complete response.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2652-z) contains supplementary material, which is available to authorized users.

Optimal outcomes for liver-dominant metastatic breast cancer with transarterial chemoembolization with drug-eluting beads loaded with doxorubicin

The purpose of this study was to evaluate the efficacy of image-guided delivery of locoregional chemotherapy to breast cancer hepatic metastases using doxorubicin-loaded drug-eluting beads (DEBDOX). An IRB-approved multi-center, prospective, open, non-controlled repeat treatment registry to investigate the safety and efficacy of doxorubicin microspheres in the treatment of patients with unresectable liver metastasis from breast cancer was reviewed. Statistical analysis was performed with differences of P < 0.05 considered significant. About 40 patients with metastatic breast cancer (MBC) to the liver underwent a total of 75 image-guided procedures with hepatic arterial drug-eluting beads loaded with doxorubicin (DEBDOX). Treatment was well tolerated with a total of eight patients sustaining 13 adverse events within the 30 days of each treatment session. All adverse events were either a grade I or grade II in toxicity. After a median follow-up of 12 months in all patients, the hepatic progression-free survival was a median of 26 months and overall survival was a median of 47 months. The treatment of hepatic metastasis from MBC using DEBDOX is an effective local therapy with very high response rates and a very safe toxicity profile. In comparison to chemotherapy alone, consideration of hepatic-directed therapy is warranted in patients with liver-dominant metastatic disease.

Effects on the visual system might contribute to some of the cognitive deficits of cancer chemotherapy-induced 'chemo-fog'

The diminution in certain aspects of cognitive function that is reported to occur in some patients during or after adjuvant cancer chemotherapy is variously known as 'chemo-fog', 'chemo-brain' or other such term. In addition to reported deficits in attention, concentration and other functions, most, if not all, of the studies report deficits involving visual-spatial function or visual memory. Since the visual system is part of the nervous system, it seems reasonable to ask if it is susceptible to some of the deleterious effects produced by adjuvant chemotherapeutic drugs. We propose here the possibility that some portion of the vision-related aspects of the 'chemo-fog' spectrum of cognitive deficits results from a direct action of the adjuvant drugs on the visual system or from drug/drug or site/site interaction between effects on the visual system and other critical brain regions.

Dose-escalation phase I study in metastatic breast cancer patients with combination of paclitaxel and tegafur·uracil

The study present the results of the dose-setting study of concomitant weekly administration of paclitaxel and tegafur·uracil (UFT) for metastatic breast cancer. Eligible patients who entered the study underwent two or more courses of weekly paclitaxel + UFT therapy as the protocol therapy. The initial dose (level 1) was paclitaxel, 80 mg/m(2) and UFT, 400 mg/day. At level 2, paclitaxel remained the same, but UFT was increased to 600 mg/day. At level 3, only paclitaxel was increased to 90 mg/m(2). Twelve patients were enrolled in this study between September 2000 and September 2002. Three patients were assigned to level 1. Grade 3 liver dysfunction (increased aspartate aminotransferase and alanine aminotransferase) was noted in one patient and grade 4 neutropenia was noted in one patient, showing that dose-limiting toxicity was detected in 2/3 patients. In accordance with the protocol, UFT was fixed at 400 mg/day and paclitaxel was decreased to 60 mg/m(2) at level -1, and then increased to 70 mg/m(2) at level 0. The overall effective rate after completion of two courses was 33% (3/9) including one case of complete response and two cases of partial responses. The remaining patients presented with stable diseases and no patient had progressive disease. In this study, weekly paclitaxel with concomitant UFT was administered. The recommended doses of paclitaxel and UFT were determined to be 70 mg/m(2) and 400 mg/day, respectively. As the toxicity profile shows, the highest toxicity level of this regimen was neutropenia and liver dysfunction, and dose-limiting toxicity was neutropenia.

Safety and Feasibility of Carboplatin and Paclitaxel followed by Fluoropyrimidine Analogs and Radiation as Adjuvant Therapy for Gastric Cancer

Background

Adjuvant 5-fluorouracil (5FU)-based chemo-radiotherapy is currently considered a standard of care for the treatment of gastric cancer. The impact of 5FU-based adjuvant therapy on the rate of distant recurrence has been modest. In order to improve the systemic effects of adjuvant therapy, we have been treating patients with resected gastric cancer with carboplatin and paclitaxel followed by fluoropyrimidine analogue and radiation.

Methods

We report on the outcomes of 21 consecutive gastric cancer patients treated off protocol with adjuvant carboplatin (area under the curve 5 mg/ml × min) and paclitaxel (175–200 mg/m²) every 3 weeks, followed by concurrent pyrimidine analogs (either capecitabine 1,600–2,000 mg/m²/day in 17 patients, or 5FU 200 mg/m²/day in 4 patients) and radiation (45–50.4 Gy). Patients received a total of 4–6 cycles of carboplatin and paclitaxel.

Results

The median age at diagnosis was 60 years. Sixteen patients had stage 3 disease and 7 of them had positive surgical margins (6 with R1 and 1 with R2 resection), 3 patients were stage 2, and 2 patients were stage 1 (all had R0 resection). All patients had D1/D2 (4 had D2 and 17 had D1) lymph node dissection. The incidence of grade 3 or higher overall, hematologic, or gastrointestinal toxicity in the patients receiving carboplatin and paclitaxel was 57, 48 and 10%, respectively. No treatment-related deaths were observed. After adjuvant treatment 15 patients developed recurrent disease, 10 of whom had distant metastases. The median recurrence-free survival (RFS) was 12.3 months. The median overall survival (OS) was 16.0 months. Patients with R0 resection had significantly longer OS than did those with positive surgical margins (log-rank p = 0.0060). Median OS for the R0 resection group was 28.8 months.

Conclusions

Carboplatin and paclitaxel added to radiation plus fluoropyrimidine analogs is a well-tolerated regimen in the adjuvant setting. The activity of this regimen in this relatively high-risk group of gastric cancer patients is of interest for future development.

A phase I and pharmacokinetic study of ixabepilone in combination with Carboplatin in patients with advanced solid malignancies

PURPOSE

To determine the recommended phase II dose of combination ixabepilone plus carboplatin based on the maximum tolerated dose, pharmacokinetics, optimum schedule, and safety.

EXPERIMENTAL DESIGN

Patients with advanced solid malignancies were treated with escalating doses of carboplatin plus ixabepilone administered on day 1 (schedule A) or days 1 and 8 (schedule B) of a 21-day cycle. Blood was sampled during cycle 1 for pharmacokinetic analysis of ixabepilone (both schedules) and carboplatin (schedule B).

RESULTS

Fifty-two patients were treated with ixabepilone doses ranging from 30 to 50 mg/m2 per 21-day cycle plus carboplatin area under curve (AUC) 5 or 6 (Calvert formula). On schedule A (ixabepilone 40 mg/m2 over 1 hour plus carboplatin AUC 6), 2 of 2 patients experienced dose-limiting toxicity (DLT). On schedule B (ixabepilone 25 mg/m2 over 1 hour on days 1 and 8 plus carboplatin AUC 6), 3 of 3 patients experienced DLT. DLT was myelosuppression; however, cumulative sensory neuropathy limited extended dosing on schedule A. Ixabepilone and carboplatin pharmacokinetics were similar to those using either drug as monotherapy, indicating an absence of pharmacokinetic drug interactions. Based on DLTs and tolerability with repeated dosing, the recommended doses were 30 mg/m2 ixabepilone (1-hour infusion) d1 q3w plus carboplatin AUC 6 (schedule A) and 20 mg/m2 ixabepilone (1 hour infusion) d1, d8 q3w plus carboplatin AUC 6 (schedule B).

CONCLUSIONS

Data from the present study show the feasibility and tolerability of combination ixabepilone plus carboplatin, with ixabepilone administered on day 1 or on days 1 and 8 on a 21-day cycle.

Docetaxel and carboplatin combination chemotherapy as outpatient palliative therapy in carcinoma of unknown primary: a multicentre Hellenic Cooperative Oncology Group phase II study

INTRODUCTION

Taxane/platinum combinations exhibit synergistic cytotoxicity and activity against a broad range of solid tumours. We sought to optimise the regimen as a suitable outpatient palliative treatment for cancer of unknown primary (CUP).

PATIENTS AND METHODS

Eligible CUP patients with adenocarcinoma or poorly differentiated carcinoma, performance status of 0-2, adequate organ function and assessable disease were treated with docetaxel 75 mg/m(2) and carboplatin at an area under the concentration time-curve (AUC) of 5, both as 30-minute intravenous infusions, every three weeks. Patients with isolated axillary adenopathy, squamous cell cervical or inguinal adenopathy and PSA or germ-cell serum tumour markers were excluded.

RESULTS

Forty-seven patients entered the trial, 24 with predominantly nodal disease or non-mucinous peritoneal carcinomatosis (favourable risk) and 23 with visceral metastases (unfavourable risk). A median of 6 cycles of chemotherapy were administered, with relative dose intensities of both drugs >90%. Response rates were 32% (46% in favourable risk, 17% in unfavourable), comparable to the activity of paclitaxel/platinum regimes, though complete remissions were seen only in favourable risk patients. Granulocyte-colony stimulating factor support was used in a third of treatment cycles. Toxicity was mild and manageable, with grade 3-4 neutropenia in 26% of patients, febrile neutropenia in 7% and severe non-hematologic side-effects in less than 8% of patients. No toxic deaths or severe neurotoxicity were seen. Median time to progression (TTP) and overall survival (OS) were 5.5 and 16.2 months respectively. Survival was driven mainly by favourable-risk patients (22.6 months), as those with visceral metastases had a poor median survival of only 5.3 months. Good performance status and low-volume disease predicted for superior outcome, while docetaxel relative dose-intensity was a positive prognosticator only in favourable-risk patients.

CONCLUSIONS

One-hour docetaxel/carboplatin is a convenient, safe and effective outpatient palliative treatment for CUP patients, providing meaningful survival prolongation only in favourable-risk patients. Insights in the molecular biology of CUP are needed for the development of targeted therapeutic manipulations of malignant resistance and progression.

What can we learn from rodents about prolactin in humans?

Prolactin (PRL) is a 23-kDa protein hormone that binds to a single-span membrane receptor, a member of the cytokine receptor superfamily, and exerts its action via several interacting signaling pathways. PRL is a multifunctional hormone that affects multiple reproductive and metabolic functions and is also involved in tumorigenicity. In addition to being a classical pituitary hormone, PRL in humans is produced by many tissues throughout the body where it acts as a cytokine. The objective of this review is to compare and contrast multiple aspects of PRL, from structure to regulation, and from physiology to pathology in rats, mice, and humans. At each juncture, questions are raised whether, or to what extent, data from rodents are relevant to PRL homeostasis in humans. Most current knowledge on PRL has been obtained from studies with rats and, more recently, from the use of transgenic mice. Although this information is indispensable for understanding PRL in human health and disease, there is sufficient disparity in the control of the production, distribution, and physiological functions of PRL among these species to warrant careful and judicial extrapolation to humans.