ABSTRACT
Malignant disease is the second most frequent cause of death between the ages of 1 and 15 years. Childhood tumors are relatively more malignant and disseminate early. Cysteine proteases are proteolytic enzymes involved in many pathological processes. Cysteine protease inhibitors constitute the final regulatory step in the control of cysteine proteases. Currently, cystatin C [CC] is the most frequently investigated family member and is involved in processes such as tumor invasion and metastasis: In such diseases the emphasis is placed on the fine balance and regulation of both the cysteine proteases and their inhibitors, with an imbalance resulting in a pathological state. To assess the status of cystatin C and the effects of chemotherapy on serum CC in patients with various malignant diseases. The present study is a case-control study done at AI-Kadhimiya Teaching Hospital in [2010]. Includes measurement of serum cystatin C in 60 patients with different malignant conditions who were classified into two groups: Patients with definitely newly diagnosed malignant tumor without chemotherapy G1: [n=30]. Patients with definitely diagnosed malignant tumor on chemotherapy G2: [n=30]. The results were compared with another 30 patients complaining from diseases other than malignancy who were included as disease-unrelated controls [G3]: [n=30]. showed a significant increase in serum cystatin C in patients with malignant tumors as compared with the controls [p < 0.001]. Moreover, serum cystatin C was significantly high in patients on no treatment G1 compared with patients on chemotherapy G2; this can be explained partly on genetic basis and partly due to DMA methylation-dependent epigenetic mechanisms may play an important role during neoplastic transformation and/or tumor progression of cystatin C gene by malignant cells. Cystatin C can be used as a tumor marker in pediatric malignancy although not specific