Abstract:

Introduction: Adenosine deaminase (ADA) is a key enzyme in the purine metabolic 
pathway. Inflammatory and neoplastic conditions lead to the accumulation of extracellular 
adenosine, which probably suppresses the antitumor immune response and promotes growth. 
Objective: To determine the levels of ADA in patients with metastatic breast cancer (MBRC) and 

colorectal carcinoma (MCRC) compared to patients with stable disease with the same tumor 
processes. Material and method: The study included 95 patients with BRC (45) and CRC (50). The 
patients were diagnosed and treated at the Burgas Cancer Centre. TNM classification, stage, 
previous therapy, last PET-CT for assessment of metastases, dynamics of tumor markers were 
extracted from medical records. The study of serum ADA enzyme activity was performed using a 
test from Diazyme Laboratories, USA) with a biochemical analyzer Mindray BS220E. Standard 
statistical analysis was performed. Results: Patients were divided into group G2 with active disease 
and metastases (clinical stage III-IV) and G1 with stable disease without progression (stage II). 
ADA values in the G2 group (15.7±7.08U/L) were significantly higher (p=0.0018) compared to 
those in the G1 group (8.5±1.51U/L). ADA values were highest in patients with liver metastases 
(21.0±7.2U/L) compared to those with bone or lymph node metastases (10.86±3.43 and 11.62±2.62, 
p=0.0002, respectively). A significant positive correlation was observed between ADA activity and 
tumor stage (r=0.633; p<0.0001). Serum levels of CEA, Ca19-9, and CA15-3 were also 
significantly higher in G2 than in G1, but no correlation with ADA was observed. Conclusion: 
Serum ADA activity may be a useful biomarker for monitoring the progression of breast and 
colorectal cancer. 

Keywords: ADA, breast cancer, colorectal carcinoma, metastatic carcinoma.  

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