Abstract
Background
Breast cancer in very young women is very rare, usually have more aggressive biological characteristics, present at a later stage and is associated with a poor prognosis. It is hard to diagnosis and often late to be diagnosed. We reported a case of breast cancer in 7 years old girl who was accidentally found in operation expected to be a benign lesion.

Case Summary
A female, Asian, 7-years old complaining of a mass and enlargement in her left breast since one year prior came to the hospital. No family history of breast or ovarian cancer in primary relatives. Previous excisional biopsy in a rural hospital six months earlier revealed a 3.2 cm ductal carcinoma in situ (DIN2)with differential diagnosis of papillary ductal carcinoma. Estrogen, progesterone and Her2 receptors were negatives. Physical examination found enlargement of the left breast, unclear tumor boundaries, Ultrasound demonstrated a 4-cm mass in her upper lateral of the left breast (ACR BIRADS 5 - highly suspicious of malignancy, while no findings in her right breast. No findings on chest X-ray and abdominal ultrasound. The patient was diagnosed with ductal carcinoma of the left breast, cTisN0M0, Stage 0, karnofsky 80%. She was offered modified radical mastectomy, no chemotherapy and neither radiation therapy performed. Routine follow-up every three months was done. There were no findings on physical, chest X-ray, and abdominal ultrasound, CEA & Ca 15-3 level were average. Two years follow up remains free of recurrence.

Conclusion
Sufficient resection margins need for treatment of breast cancer in young women because it has a higher rate of local recurrence. Adjuvant treatment options may different compared with older women; there need judgment and tailoring of the treatment.

Key words: breast cancer, young women, carcinoma in situ