Background: Aldehyde dehydrogenase 1 (ALDH1) is a marker of normal and malignant human mammary stem cells that has been reported to be associated with poor prognosis. Studies on the detection of ALDH1+ cells can help the treatment of patients with breast cancer. The aim of this study was to determine the activity of ALDH1 in breast cancer and its relationship with the pathological features of the tumors.
Methods:  ALDH1 activity was studied by immunohistochemistry in 121 paraffin-embedded histological samples of breast cancer patients from Department of Pathology of Milad Hospital, Tehran, Iran during 2006-2007. The relationship of ALDH1 with the pathological features of the tumors (size, grade, lymph node metastasis and vascular invasion) was also investigated.
Results:  Eighty-five percent of breast cancer samples expressed ALDH1 in their cytoplasm with a wide range of intensity (weak, moderate and strong), while 18 samples (14.9%) were completely negative. The majority of cases (97.1%) showed ALDH1 positivity in the stroma of tumors which varied from weak (2.9%) to strong (73.5%). ALDH1 H-score (ALDH1% × intensity) of tumor cells varied from 0 to 240 (mean= 80). ALDH1 H-score was ≤80 in 62 (51.2%) and >80 in 59 (48.8%) samples. There was no statistically significant relationship between ALDH1 H-score and age (P=0.358), tumor size (P=0.375), tumor grade (P=0.207), lymph node metastasis (P=0.125) or vascular invasion (P=0.190).
Conclusion: ALDH1 activity was demonstrated in 85.1% of breast cancer samples although its level of expression was not correlated with the pathologic features of breast tumors.