Objective: Eccrine poroma is a benign appendage tumor showing either eccrine or apocrine differentiation. However, malignant transformation of this tumor is very rare. The present report demonstrated a case of the eccrine poroma with malignant transformation and its rarity in terms of its high degree of recurrences and its aggressiveness with bony invasion.
Case Report: A 67-year old female had a mass on plantar surface of 4th-5th intermetatarsal area of her left foot for 10 years with three recurrent episodes following excisions at local hospital with no pathological report. She was referred to our institute. A recurrent tumor was removed again with pathological findings as eccrine poroma with incomplete excision; however, the patient had a failure to follow-up. Four years later, she was back in our center again with 5th episode of recurrent tumor which was marginally excised with pathological findings revealing a malignant transformation of eccrine poroma with close resected margins. Unfortunately, the patient failed to follow-up again. Eventually, four years later, she returned to our institute with 6th recurrent episode of tumor. Incisional biopsy was performed with pathological findings as appendage tumor with eccrine differentiation. Wide resection including removal of 5th metatarsal head-and-neck was performed due to aggressive behaviors of this tumor; particularly; history of malignant findings and multiple recurrences, significantly bony invasion. Final pathological findings were malignant eccrine poroma with close resected margin. There were no metastases in evidence from all investigations. Local irradiation with the aim of eradication of microscopically residual tumor was initiated.
Conclusion: Malignant transformation is a rare occurrence of eccrine poroma. It should be initially included in differential diagnoses, especially in a patient with long standing foot lesion or history of recurrent masses. Wide excision is recommended as basis treatment, especially in a patient with high likelihood of recurrences or positive malignant transformation.

Keywords: Malignant eccrine poroma, Porocarcinoma, Eccrine poroma, Recurrence, Malignant transformation, Foot