Sacituzumab Govitecan in Combination With Pembrolizumab for Patients With Metastatic Urothelial Cancer That Progressed After Platinum-Based Chemotherapy: TROPHY-U-01 Cohort 3

PURPOSE

Pembrolizumab is standard therapy for patients with metastatic urothelial cancer (mUC) who progress after first-line platinum-based chemotherapy; however, only approximately 21% of patients respond. Sacituzumab govitecan (SG) is a trophoblast cell surface antigen-2-directed antibody-drug conjugate with US Food and Drug Administration-accelerated approval to treat patients with locally advanced or mUC who previously received platinum-based chemotherapy and a checkpoint inhibitor (CPI). Here, we report the primary analysis of TROPHY-U-01 cohort 3.

METHODS

TROPHY-U-01 (ClinicalTrials.gov identifier: NCT03547973) is a multicohort, open-label phase II study. Patients were CPI-naïve and had mUC progression after platinum-based chemotherapy in the metastatic setting or ≤12 months in the (neo)adjuvant setting. Patients received 10 mg/kg of SG once on days 1 and 8 and 200 mg of pembrolizumab once on day 1 of 21-day cycles. The primary end point was objective response rate (ORR) per central review. Secondary end points included clinical benefit rate (CBR), duration of response (DOR) and progression-free survival (PFS) per central review, and safety.

RESULTS

Cohort 3 included 41 patients (median age 67 years; 83% male; 78% visceral metastases [29% liver]). With a median follow-up of 14.8 months, the ORR was 41% (95% CI, 26.3 to 57.9; 20% complete response rate), CBR was 46% (95% CI, 30.7 to 62.6), median DOR was 11.1 months (95% CI, 4.8 to not estimable [NE]), and median PFS was 5.3 months (95% CI, 3.4 to 10.2). The median overall survival was 12.7 months (range, 10.7-NE). Grade ≥3 treatment-related adverse events occurred in 61% of patients; most common were neutropenia (37%), leukopenia (20%), and diarrhea (20%).

CONCLUSION

SG plus pembrolizumab demonstrated a high response rate with an overall manageable toxicity profile in patients with mUC who progressed after platinum-based chemotherapy. No new safety signals were detected. These data support further evaluation of SG plus CPI in mUC.

Primary analysis of TROPHY-U-01 cohort 3, a phase 2 study of sacituzumab govitecan (SG) in combination with pembrolizumab (Pembro) in patients (pts) with metastatic urothelial cancer (mUC) that progressed after platinum (PT)-based therapy

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Background: Pembro is standard of care for pts with mUC who progress after 1L PT therapy but only ~21% of pts respond, highlighting an unmet need (Bellmunt, et al. NEJM. 2017). SG is an antibody-drug conjugate composed of an anti-Trop-2 antibody coupled to SN-38 via a hydrolyzable linker. In Cohort 1 of the TROPHY-U-01 study, SG demonstrated a 27% objective response rate (ORR) with manageable safety in 113 pts with locally advanced or mUC who previously received PT and a checkpoint inhibitor (CPI; Tagawa, et al. J Clin Oncol. 2021), leading to accelerated FDA approval in this pt population. Preliminary results of the phase 2 TROPHY-U-01 Cohort 3 study showed that SG plus Pembro demonstrated a high ORR (34%) as a 2L therapy in 41 CPI-naive pts with mUC who progressed after PT (Grivas et al. J Clin Oncol. 2021). Here we present the primary analysis of Cohort 3. Methods: Cohort 3 pts (≥18 y) had progression of mUC following PT in the metastatic setting or following ≤12 mo of PT in the (neo)adjuvant setting and ECOG PS 0-1. Pts received 10 mg/kg of SG on D1 and D8 and 200 mg of Pembro on D1 of a 21-D cycle for ≤2 y. The primary endpoint was ORR [complete response (CR) + partial response (PR)] per central review by RECIST 1.1. Secondary endpoints include clinical benefit rate [CBR; CR + PR + stable disease for at least 6 mo], duration of response (DOR) and progression-free survival (PFS) per central review; and safety. Target enrollment was approximately 41 pts based on a Simon two-stage design for 90% power at one-sided α of 0.05 to demonstrate 21% improvement in ORR, with a null hypothesis of historical ORR ≤20% and an alternate hypothesis of ORR ≥41%. Results: As of July 26, 2022, median follow-up was 12.5 mo (range, 0.9-24.6) for treated pts (N=41); median age, 67 y (range, 46-86), 83% male, 61% ECOG PS 1, 76% ≥1 Bellmunt risk factors, and 78% visceral metastases (29% liver). Median duration of last prior anti-cancer therapy was 2.7 mo (range, 0-13). Per central review, ORR was 41% (95% CI, 26.3-57.9; 20% CR); CBR was 46% (95% CI, 30.7-62.6); median DOR was 11.1 mo (95% CI, 4.8-NE [not estimable]; n=17); and median PFS was 5.3 mo (95% CI, 3.4-10.2). Median time to response was 1.4 mo (95% CI, 1.3-2.7) and median OS was 12.7 mo (95% CI, 10.7-NE). Grade ≥3 treatment-related adverse events (TRAEs) occurred in 61% of pts; most common Grade ≥3 TRAEs were neutropenia (37%; 10% febrile neutropenia), leukopenia (20%), and diarrhea (20%). TRAEs led to a 15% discontinuation rate. Systemic steroid and G-CSF use were both 34%. No treatment-related death occurred. Conclusions: SG plus Pembro demonstrated a high ORR and CBR with a manageable safety profile in 2L mUC in CPI-naive pts who progressed after PT-based therapy. No new safety signals were observed with the combination. These data support further evaluation of SG plus CPI in mUC. Clinical trial information: NCT03547973 .

TROPHY-U-01 Cohort 3: Sacituzumab govitecan (SG) in combination with pembrolizumab (Pembro) in patients (pts) with metastatic urothelial cancer (mUC) who progressed after platinum (PLT)-based regimens

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Background: Checkpoint inhibitors (CPIs) are standard therapy for pts with mUC after PLT-based regimens, with limited long-term disease control. SG is an antibody-drug conjugate composed of an anti-trophoblast cell-surface antigen 2 (Trop-2) antibody coupled to SN-38 (a topoisomerase-I inhibitor) via a proprietary hydrolyzable linker. In the TROPHY-U-01 registrational phase 2 trial, SG monotherapy demonstrated significant activity and manageable safety in pts with mUC who progressed after prior PLT-based chemotherapy and CPI, with 27% objective response rate (ORR) and median overall survival of 11 months (Tagawa, et al. J Clin Oncol. 2021). Here, we present interim efficacy and safety results of combining SG with Pembro as 2nd-line therapy in CPI-naive pts with mUC who progressed after PLT-based chemotherapy (cohort 3). Methods: TROPHY-U-01 is a multicohort, open-label, global phase 2 trial. Eligible pts had measurable disease, Eastern Cooperative Oncology Group performance status (ECOG PS) 0–1, and creatinine clearance ≥30 mL/min. The recommended phase 2 dose (RP2D) was determined during a 10-pt safety lead-in, and additional pts were enrolled at the RP2D in a Simon 2-stage design. Primary endpoint: ORR by blinded independent central review per Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST 1.1). Key secondary endpoints: investigator-assessed ORR, clinical benefit rate [CBR; complete response (CR) + partial response (PR) + stable disease], progression-free survival (PFS), and safety. Results: At the time of data cutoff, 41 pts received at least a dose of SG at the RP2D (10 mg/kg). Of these 41 pts, median (range) age was 67y (46–86), 83% men, 61% ECOG PS 1, 76% had ≥1 Bellmunt risk factor, and median (range) number of prior anticancer regimens was 1 (1–3). At a median follow-up of 5.8 mo, the investigator-assessed ORR was 34% (95% CI, 20.1–50.6; 1 CR; 13 PR); CBR was 44% (95% CI, 28.5–60.3); 6-mo PFS rate was 47%. Median time to response was 2.0 mo (95% CI, 1.3–2.8). Most common treatment-emergent adverse events (TEAEs) were diarrhea (76%), nausea (59%), anemia (56%), neutropenia (44%), and asthenia (41%). Treatment-related grade ≥3 AEs occurred in 59% of pts. Key grade ≥3 TEAEs of any cause included diarrhea (24%), anemia (20%), febrile neutropenia (10%), fatigue (7%), and asthenia (5%). Two pts discontinued treatment due to treatment-related AEs. No treatment-related death occurred. Conclusions: SG in combination with Pembro demonstrated encouraging ORR and CBR, with an overall manageable safety profile with no new safety signal in CPI-naive pts who progressed after prior PLT-based chemotherapy. The data support further evaluation of SG plus CPI in mUC. Limitations: small sample size, short follow-up, and lack of randomization. Biomarker evaluation is ongoing. Clinical trial information: NCT03547973.

TROPHY-U-01 cohort 4: Sacituzumab govitecan (SG) in combination with cisplatin (Cis) in platinum (PLT)-naïve patients (pts) with metastatic urothelial cancer (mUC)

TPS581

Background: Cis-based combination chemotherapy regimens with gemcitabine or methotrexate, vinblastine, and doxorubicin are commonly used as initial treatment for mUC. However, only a fraction of pts maintain a durable response. Alternative Cis-based combinations with improved efficacy while maintaining tolerability are needed. SG is an antibody-drug conjugate (ADC) composed of an anti-trophoblast cell-surface antigen-2 (Trop-2) antibody coupled to SN-38 (a topoisomerase-I inhibitor) via a proprietary hydrolyzable linker. In vitro/in vivo urinary bladder cancer models suggest that the combination of SG and Cis resulted in additive antitumor activity over either agent alone (data on file). In the phase 2 registrational TROPHY-U-01 study, SG monotherapy resulted in a 27% objective response rate (ORR) and a median overall survival (OS) of 10.9 months with a manageable, mostly non–Cis-overlapping toxicity profile in heavily pretreated pts with mUC (Tagawa et al, J Clin Oncol. 2021). These results led to accelerated approval of SG by the FDA in 2021 for pts with locally advanced or mUC who previously received PLT-containing chemotherapy and a checkpoint inhibitor. We hypothesized that SG and Cis in combination may improve efficacy/safety over available first-line mUC regimens. TROPHY-U-01 Cohort 4 study will evaluate the safety, tolerability, and clinical activity of this novel combination. Methods: TROPHY-U-01 (NCT03547973) is a multicohort, open-label, global phase 2 trial. Cohort 4 will evaluate combination SG and Cis in PLT-naive pts with mUC or unresectable locally advanced disease. Key eligibility requirements include Eastern Cooperative Oncology Group performance status 0–1; no prior anticancer monoclonal antibody or ADC therapy within 4 weeks of study drug initiation; no history of active interstitial lung disease or noninfectious pneumonitis; adequate hematologic, hepatic, and renal function. Pts will be treated with Cis at 70 mg/m2 on day 1 of a 21-day cycle (if creatinine clearance [CrCl] ≥60 mL/min) or at a split dose of Cis at 35 mg/m2 on days 1 and 8 of a 21-day cycle (if CrCl 50-59 mL/min) followed by SG (5, 7.5, or 10 mg/kg) on days 1 and 8 of a 21-day cycle. The recommended phase 2 dose will be the dose in which ≤30% dose-limiting toxicities are noted in cycle 1. Combination therapy will continue for up to 6 cycles, followed by SG and avelumab maintenance given until progression. Prophylactic granulocyte colony-stimulating factor is not allowed in cycle 1 of the safety lead-in phase. Primary endpoint is ORR per RECIST v1.1 by blinded independent central review (BICR). Secondary endpoints include progression-free survival, duration of response, and clinical benefit rate per BICR and investigator assessment. OS and safety will be assessed. Enrollment is ongoing; ̃60 pts expected across ̃30 sites in North America and Europe. Clinical trial information: NCT03547973.

TROPiCS–03: A phase II open-label study of sacituzumab govitecan (SG) in patients with metastatic solid tumors

TPS3648

Background: Trophoblast cell surface antigen (Trop-2) is highly expressed in many epithelial cancers (non–small-cell lung cancer [NSCLC], endometrial cancer, urothelial carcinoma [UC], and triple-negative breast cancer [TNBC]) and has been linked to aggressive disease and poor prognosis. SG is a Trop-2–directed antibody drug conjugate containing SN-38 (active metabolite of irinotecan) with a 7.5:1 drug-to-antibody ratio and unique hydrolyzable linker that allows for extracellular bystander effect. The phase 1/2 IMMU-132-01 basket study reported clinical activity with SG in patients with multiple tumor types not selected for Trop-2 expression including NSCLC (objective response rate [ORR]: 17%), TNBC (ORR: 33%), and UC (ORR: 31%).1-3 Results from the overall safety population (N=420) from this study found that SG was tolerable, with a predictable and manageable safety profile, and low discontinuation rates due to AEs. Methods: To test a biomarker-enrichment strategy with Trop-2, the TROPiCS-03 (TROP-2 Investigations in Cancer with SG) study was initiated. TROPiCS-03 (NCT03964727) is a multi-cohort, open-label, phase 2 study in patients with metastatic solid tumors - presently NSCLC (adenocarcinoma and squamous cell carcinoma), head and neck squamous cell carcinoma, and endometrial cancer - selected based on elevated Trop-2 expression by a validated IHC assay. Patients receive SG (10 mg/kg IV, days 1 and 8 every 21 days) and continue treatment until lack of clinical benefit or unacceptable toxicity. The primary endpoint is objective response rate (local assessment) and additional endpoints include clinical benefit rate, duration of response, progression-free survival, and safety. Females or males ≥18 years old who are histologically documented to have locally advanced or metastatic (M1, stage 4) solid tumors of the above types are eligible. Patients must have ECOG 0 or 1 and adequate clinical laboratory results to be enrolled. All subjects will have progressed after prior platinum-based chemotherapy and programmed death-ligand 1 (PD-L1) or programmed cell death protein 1 (PD-1) directed therapy. Patients who have previously received topoisomerase I inhibitors and those with known active CNS metastases are excluded. Approximately 160 patients will be enrolled in the trial overall; enrollment in the NSCLC cohort is currently in progress. References: Heist RS et al. J Clin Oncol. 2017;35:2790-7, Bardia A et al., NEJM. 2019;380:741-51.,Tagawa ST et al., Oral presentation; ASCO-GU 2019, San Francisco, CA. Clinical trial information: NCT03964727 .

Impact of qnrA1, qnrB1 and qnrS1 on the efficacy of ciprofloxacin and levofloxacin in an experimental pneumonia model caused by Escherichia coli with or without the GyrA mutation Ser83Leu

OBJECTIVES

The aim of this study was to evaluate the impact of qnrA1, qnrB1 and qnrS1 on the in vivo efficacies of ciprofloxacin and levofloxacin in an experimental model of pneumonia caused by Escherichia coli.

METHODS

Two isogenic groups of E. coli transformants, based on two ATCC 25922 strains, with or without the GyrA mutation Ser83Leu, and carrying qnrA1, qnrB1 or qnrS1, were used in an experimental pneumonia model. The efficacies of ciprofloxacin (40 mg/kg/day) and levofloxacin (50 and 150 mg/kg/day) were evaluated.

RESULTS

For the pneumonia caused by the parental strains lacking qnr genes, both fluoroquinolones significantly (P<0.05) reduced the bacterial lung concentration by >7 log10 cfu/g against E. coli ATCC/pBK and between 5.09 and 6.34 log10 cfu/g against E. coli ATCC-S83L/pBK. The presence of any qnr genes in the strains of both isogenic groups diminished the reduction of bacterial lung concentration with any therapy (P<0.05). Furthermore, all therapeutic schemes reduced the percentage of positive blood cultures in both isogenic groups (P<0.05). Finally, the survival results suggest a higher mortality with the strains expressing qnr genes.

CONCLUSIONS

The presence of qnrA1, qnrB1 and qnrS1 in E. coli reduced the efficacy of ciprofloxacin and levofloxacin in a murine pneumonia model.

Efficacy of rifampin, in monotherapy and in combinations, in an experimental murine pneumonia model caused by panresistant Acinetobacter baumannii strains

The objective of this work was to evaluate the efficacy of rifampin, and its combinations with imipenem or sulbactam, in an experimental pneumonia model caused by two panresistant Acinetobacter baumannii strains (HUVR99 and HUVR113). Minimum inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) (μg/ml) of the strains were rifampin 128/>128 for both strains, imipenem 128/>256 and 256/>256 for HUVR99 and HUVR113, respectively, and sulbactam >256/>256 for both strains. In time-kill studies, at MICs, rifampin was bactericidal for both strains and sulbactam against the HUVR99 strain. Rifampin plus imipenem or sulbactam, at the MIC or mice C (max), were synergistic. In vivo, against HUVR99 and HUVR113, rifampin (73% and 40%) and its combinations improved the survival with respect to the control group (20% and 0%, p < 0.05), respectively. Rifampin (87% and 46%) and its combinations improved the sterilization of blood cultures with respect to the control groups (0%, p < 0.05). In regard to the bacterial clearance from lungs, rifampin (2.57 ± 2.47 and 5.35 ± 3.03 log(10) cfu/g) and its combinations with imipenem or sulbactam diminished the bacterial lung concentration with respect to the control group (10.89 ± 3.00 and 11.86 ± 0.49, p < 0.05) with both strains. In conclusion, rifampin alone or associated to imipenem or sulbactam were effective for the treatment of murine pneumonia caused by selected panresistant A. baumannii strains.

Activity of cefepime and carbapenems in experimental pneumonia caused by porin-deficient Klebsiella pneumoniae producing FOX-5 beta-lactamase

The in-vivo activities of cefepime, imipenem and meropenem against the porin-deficient strain Klebsiella pneumoniae C2 and its derivative K. pneumoniae C2(pMG252) coding for the AmpC-type beta-lactamase FOX-5 were determined. Bactericidal activities were determined with the kill-curve method. A pneumonia model in guinea-pigs was developed, and Cmax, t(1/2) and DeltaT/MIC were calculated for the three agents tested. Animals were treated for 72 h with sterile saline (control group) or with cefepime, imipenem or meropenem (240 mg/kg/day, intramuscularly, three times daily). Bacterial counts in lungs (log10 CFU/g tissue) were determined by serial dilution. MICs (mg/L) of cefepime, imipenem and meropenem against K. pneumoniae C2/K. pneumoniae C2(pMG252), determined by macrodilution, were: 0.5/4, 0.5/0.5 and 0.25/0.5, respectively. Bacterial counts in the lungs of animals infected with K. pneumoniae C2 and treated with antimicrobial agents were always lower than in the control group (cefepime, 4.4 +/- 0.5; imipenem, 4.6 +/- 0.4; meropenem, 4.7 +/- 0.5; control group, 5.6 +/- 0.8; p <0.01). No significant differences were observed among the groups receiving therapy (p >0.05). Bacterial lung clearance was higher in treated animals than in control animals following infection with K. pneumoniae C2(pMG252) (cefepime, 4.5 +/- 0.4; imipenem, 4.0 +/- 0.3; meropenem, 4.6 +/- 0.4; control group, 6.1 +/- 0.6; p <0.01), with imipenem producing better clearance than either cefepime or meropenem (p <0.05). Thus, in the guinea-pig pneumonia model, cefepime, imipenem and meropenem were each effective against the porin-deficient K. pneumoniae strain C2 and its derivative expressing the plasmid-mediated AmpC type beta-lactamase FOX-5.

Pharmacokinetic/pharmacodynamic assessment of the in-vivo efficacy of imipenem alone or in combination with amikacin for the treatment of experimental multiresistant Acinetobacter baumannii pneumonia

A guinea-pig pneumonia model involving imipenem-susceptible and imipenem-resistant strains of Acinetobacter baumannii was developed to assess the in-vitro and in-vivo activities of imipenem, alone or in combination with amikacin, and the pharmacokinetic and pharmacodynamic parameters. Serum levels were measured by bioassay (imipenem) or immunoassay (amikacin), followed by calculation of pharmacokinetic and pharmacodynamic parameters (Cmax, AUC, t1/2, Cmax/MIC, AUC/MIC, and Deltat/MIC). In-vivo efficacy was evaluated by comparing bacterial counts in the lungs of treatment groups with end-of-therapy controls by anova and post-hoc tests. Decreases in the Cmax (13.4%), AUC (13%), t1/2 (25%) and Deltat/MIC (11.8-32.2%) of imipenem were observed when it was administered with amikacin, compared with administration of imipenem alone. Similarly, decreases in the Cmax (34.5%), AUC (11.6%), Cmax/MIC (34.5%) and AUC/MIC (11.7%) of amikacin were observed when it was administered with imipenem. Bacterial counts in lungs were reduced by imipenem (p 0.004) with the imipenem-susceptible strain, and by amikacin (p 0.001) with the imipenem-resistant strain. The combination of imipenem plus amikacin was inferior to imipenem alone with the imipenem-susceptible strain (p 0.01), despite their in-vitro synergy, and was inferior to amikacin alone with the imipenem-resistant strain (p < 0.0001). In summary, combined use of imipenem with amikacin was less efficacious than monotherapy, probably because of a drug-drug interaction that resulted in decreased pharmacokinetic and pharmacodynamic parameters for both antimicrobial agents.

Morphological changes induced by imipenem and meropenem at sub-inhibitory concentrations in Acinetobacter baumannii

Abstract Sub-inhibitory concentrations of imipenem and meropenem were evaluated for their ability to induce morphological changes with six strains of Acinetobacter baumannii isolated from patients with nosocomial pneumonia. Three strains were susceptible and three were resistant to carbapenems. The strains were grown in the presence of 0 (controls), 0.25x, 0.5x and 1x the MIC of both carbapenems for 4 h, and then examined after Gram's stain. Cells > or = 3 microm in size (spheroplasts) were considered to be altered. Both carbapenems induced significant numbers of spheroplasts compared to controls. Imipenem had more effect against susceptible strains, while meropenem had a greater effect against resistant strains.

Colistin efficacy in an experimental model of Acinetobacter baumannii endocarditis

The in-vivo activity of colistin was evaluated in an experimental rabbit model of Acinetobacter baumannii endocarditis with a strain susceptible to colistin and intermediate to imipenem. Compared to a control group, colistin was effective (p < 0.05) in bacterial clearance from blood and in the sterilisation of blood cultures, but was not effective in clearing A. baumannii from vegetations. Thus, although colistin may be effective in treating bacteraemia caused by susceptible strains of A. baumannii, it may not be a suitable treatment for endocarditis, perhaps because of poor penetration into vegetations and a low C(max)/MIC ratio in tissue.

Sulbactam efficacy in experimental models caused by susceptible and intermediate Acinetobacter baumannii strains

Sulbactam and imipenem were compared in an experimental pneumonia model in immunocompetent mice, using a susceptible strain of Acinetobacter baumannii, and in an experimental endocarditis model in rabbits, using an intermediately susceptible strain. In the former, sulbactam was as efficacious as imipenem in terms of survival, sterility of lungs and in the bacterial clearance from lungs and blood, provided that the t > MIC for sulbactam (1.84 h) was similar to that for imipenem (2.01 h). In the endocarditis model, imipenem (t > MIC, 2.12 h) was more efficacious than sulbactam (t > MIC, 1.17 h) in bacterial clearance from vegetations. These results show the efficacy of sulbactam in infections caused by susceptible strains of A. baumannii, with an MIC up to 4 mg/L, provided that doses reach a t > MIC similar to that of imipenem. The activity of sulbactam was time dependent.

Imipenem, doxycycline and amikacin in monotherapy and in combination in Acinetobacter baumannii experimental pneumonia

Acinetobacter baumannii is a common cause of nosocomial pneumonia and other nosocomial infections. Multiresistant A. baumannii has also a high prevalence, which can make effective treatment difficult. We designed a new model of A. baumannii experimental pneumonia using C57BL/6 immunocompetent mice. This model was used to compare the efficacy of imipenem, doxycycline and amikacin in monotherapy, and the combination of imipenem plus amikacin and doxycycline plus amikacin. Doxycycline plus amikacin were synergic in vitro after 24 h incubation, whereas imipenem plus amikacin showed no in vitro synergy. The number of sterile lungs and the lung clearance of A. baumannii were greater in the group treated with imipenem than in those treated with amikacin or doxycycline in monotherapy (P < 0.05). The combination of imipenem plus amikacin and doxycycline plus amikacin was no more effective than imipenem alone in the clearance of organisms from lungs (2.42 +/- 1.46 cfu/g versus 2.7 +/- 1.5 cfu/g versus 1.23 +/- 1.02 cfu/g). These results suggest that the addition of amikacin does not improve the results obtained by imipenem monotherapy. Doxycycline plus amikacin is an alternative to imipenem in the therapy of A. baumannii pneumonia.

Posttreatment follow-Up of brucellosis by PCR assay

In order to evaluate the usefulness of a peripheral blood PCR assay in the posttreatment follow-up of brucellosis, a cohort of 30 patients was studied by means of blood cultures, rose Bengal, seroagglutination, Coombs' antibrucella tests, and PCR assay at the time of diagnosis, at the end of treatment, and 2, 4, and 6 months later. Of the 29 patients whose PCR assays were initially positive, 28 (96.5%) were negative at the conclusion of the treatment. PCR was positive for the two patients who had relapses and negative for another four who had suspected but unconfirmed relapses. PCR was negative for 98.3% of the follow-up samples from those patients who had a favorable evolution. In conclusion, PCR appears to be a very useful technique, not only for the initial diagnosis of the disease, but also for posttreatment follow-up and the early detection of relapses.