Malignant Nodular Hidradenoma of the Left Knee: A Malignant Mystery With an Overview of Literature.

Malignant nodular hidradenoma is a rare eccrine sweat gland neoplasm characterized by recurrence, metastasis, and a locally aggressive course. In our case report, a 74-year-old man presented with a seemingly benign swelling which was persistent for the last 30 years, which was excised at an outside institute. Since the patient presented to the hospital during the peak of the pandemic, considering the age of the patient, the pandemic situation, the logistics of radiotherapy during such a situation, preserving the knee joint function in view of close proximity of the tumour to the joint, it was decided to keep the patient on follow up and continue expectant management. After a follow-up period of 24 months, no locoregional recurrence or metastasis has been observed. The patient is on annual follow-up with clinical examination and PET-CECT imaging.