BACKGROUND Metaplastic breast cancer (MpBC) is an extremely rare, therapeutically recalcitrant and aggressive variant of triple negative breast cancer (TNBC). We have previously shown molecular alterations in inducible nitric oxide (iNOS) signaling in MpBC is associated with worse overall survival. Preclinical models have shown pan-NOS inhibitor NG-monomethyl-L-arginine (L-NMMA) reduces tumor growth and epithelial to mesenchymal transition in mesenchymal cell lines. We have also previously shown in TNBC patients treated with LNMMA and docetaxel, the non-responders have a higher expression of M2 macrophage vs the responders have decreased pro-tumor N2 neutrophils at the end of therapy. Here, we report the results of L-NMMA plus taxane in a cohort of MpBC patients. METHODS We conducted a phase 1B/2 trial, with L-NMMA (starting dose of 7.5 mg/kg which was escalated to recommended phase 2 dose of 20 mg/kg) and docetaxel (100 mg/m2) every 3 weeks. Daily amlodipine was given to prevent hypertension from L-NMMA. Primary objective was to assess clinical benefit rate (CBR), as assessed by the Response Evaluation Criteria in solid tumors (RECIST). Secondary objectives were to study overall response rate (ORR), progression free survival (PFS), overall survival (OS), dose limiting toxicities (DLT), response correlation with type of MpBC, body mass index (BMI) and ethnicity. Exploratory analysis included immune correlates for clinical response; staining for iNOS, M2 macrophages (CD 68, CD 163), N2 neutrophils (CD 15, arginase), immune infiltration (PD-L1, CD 8) and fibrosis marker (α- SMA). Fisher’s exact test was used to find the association between different patient’s characteristics and the main outcome. A p-value of 0.05 was considered statistically significant and all analyses were conducted using Stata V16.1 (StataCorp, College Station, Texas 77845 USA) RESULTS Of the total 35 TNBC patients recruited, 15 patients had MpBC (Phase 1B, n= 4; Phase 2, n=11); 86.6% (13/15) patients had metastatic breast cancer (MBC), with a median of 2 prior lines of therapy (range 0-5) and 13.3% (2/15) had anthracycline-refractory locally advanced breast cancer (LABC). The CBR was 40% (6/15); the ORR was 20% (3/15) with 1 PR in MBC , 1 pathological CR and 1 PR in LABC. Grade 3 or more toxicity was seen in 13.3% (2/15) patients; however, none was attributed to L-NMMA. The mPFS and mOS for MBC patients were 4.5 months (range 3-7m) and 12.8 months, respectively. The response was more likely to be in women of Caucasian ethnicity, BMI> 25 and non-spindle pathological features such as squamous differentiation, keratinized and myxo-chondroid tumors; albeit these were not statistically significant (Table 1). CONCLUSIONS Inhibition of iNOS pathway in MpBC is a promising and novel therapeutic option in this very challenging breast cancer subtype. The small study size is an impediment in identifying clinical factors which can predict a response. This warrants further evaluation of treatment with L-NMMA in chemo-refractory MpBC patients in a larger clinical trial.

Table 1.

Association between ethnicity, BMI and pathological characteristics with response

TotalNo responderResponderp-value
N=13N=7N=6
Ethnicity    0.19 
Caucasian 10 (76.92%) 4 (57.14%) 6 (100.00%)  
Other 3 (23.08%) 3 (42.86%) 0 (0.00%)  
Obesity    1.00 
<25 BMI 3 (23.08%) 2 (28.57%) 1 (16.67%)  
>=25 BMI 10 (76.92%) 5 (71.43%) 5 (83.33%)  
Pathological features    0.27 
Spindle 5 (38.46%) 4 (57.14%) 1 (16.67%)  
Other 8 (61.54%) 3 (42.86%) 5 (83.33%)  
TotalNo responderResponderp-value
N=13N=7N=6
Ethnicity    0.19 
Caucasian 10 (76.92%) 4 (57.14%) 6 (100.00%)  
Other 3 (23.08%) 3 (42.86%) 0 (0.00%)  
Obesity    1.00 
<25 BMI 3 (23.08%) 2 (28.57%) 1 (16.67%)  
>=25 BMI 10 (76.92%) 5 (71.43%) 5 (83.33%)  
Pathological features    0.27 
Spindle 5 (38.46%) 4 (57.14%) 1 (16.67%)  
Other 8 (61.54%) 3 (42.86%) 5 (83.33%)  

Data are presented as n (%). *P-value from Fisher’s exact test. The 2 patients with adverse events were excluded from the analysis.

Citation Format: Akshjot Puri, Adriana Ordonez, Ann C. Anselme, Liliana Guzman, Polly Niravath, Jenny C. Chang. Phase 1B/2 clinical trial targeting nitric oxide in the treatment of chemo-refractory metaplastic triple-negative breast cancer patients [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-17-07.