Digital metastasis in a patient with squamous cell anal cancer

Abstract

This is a 69-year-old female with a history of squamous cell carcinoma of the anal canal who presented with a two week history of a mass at the base of the right fifth digit (pinky finger) with foul smelling discharge (Figure 1A). Five months prior, she noticed a small bruise in the area and related it to a recent trauma. She was initially diagnosed with localized anal cancer in 2012 and treated with concurrent chemoradiation. In 2015, she was found to have two lung metastases and had wedge resections for both diagnosis and treatment of metastatic disease. Unfortunately, she progressed in the lung and received several chemotherapy regimens and most recently immunotherapy with Nivolumab (anti-PD-L1). However, Nivolumab caused severe autoimmune hypothyroidism, significant facial and lower extremity swelling. To work up the pinky finger lesion, she had X-rays (Figure 1B and 1C) in February 2018 which showed a heterogeneously dense and lobulated mass with extension into the dorsal soft tissue and associated swelling with near complete destruction of the fifth distal phalanx. Differential diagnosis remained broad and included trauma, infection such as abscess, osteomyelitis, or paronychia, unreported autoimmune reaction to novel biologics such as Nivolumab, a subungal melanoma, or digital metastasis. Amputation of the fifth phalanx showed poorly differentiated carcinoma with basaloid squamous features morphologically consistent with her primary anal cancer. Both the anal biopsy and finger amputation specimens had strong diffuse immunohistochemical p16 expression, indicating human papillomavirus (HPV) positivity. The tumor cells also stained positive with P63 and CK5/6 and negative with CK7, CK20, synaptophysin, chromogranin and CD56, supporting metastatic squamous cell with basaloid features originating from the anus. She had an excellent cosmetic and functional result from the surgery (Figure 1D) and is alive now after seven months follow up.