Absolute Lymphocyte Count as a Prognostic Factor for Merkel Cell Carcinoma

Abstract

The incidence of Merkel Cell Carcinoma (MCC) is increased in immunocompromised patients. We report the prognostic impact of a simple, easy to test laboratory value, absolute lymphocyte count (ALC), as a surrogate of immune status for patients treated for MCC from 1992 to 2010. One hundred twenty-four patients treated for MCC were identified. The population for this study is composed of the 64 patients who had a complete blood count with differential recorded in the month prior to definitive surgery, chemotherapy, or radiation. Clinical and outcome characteristics were obtained from chart review. An ALC of 1.5 k/mm3 was defined as the cut point based on review of outcomes and is our laboratory's lower limit of normal. Statistical analysis was performed utilizing log rank test and a Cox proportional hazards model. Endpoints of overall survival (OS) and disease-free survival (DFS) from the time of diagnosis were calculated. Of the 64 patients, 40 were men and 61 were white. AJCC stage at presentation was: I (41%), II (14%), III (39%), and IV (6%). The most common primary site of disease was head and neck (41%), lower extremity (27%), and upper extremity (23%). Chemotherapy was given to 35% of patients and 75% received radiation therapy. For the cohort, 23 patients had an ALC <1.5 k/mm3. They were more likely men (p < 0.01), more likely received chemotherapy (p = 0.03), and had a higher AJCC stage (p = 0.03) than the ALC ≥1.5 k/mm3 group. Otherwise, there was no significant difference between the groups with regard to primary location, surgery type, radiation therapy, smoking history, alcohol use, race, or family history. The median OS for patients with an ALC <1.5 k/mm3 was 25.2 months versus 96.8 months for those with an ALC ≥1.5 k/mm3 (p = 0.0033). DFS at 60 months for those patients with an ALC <1.5 k/mm3 was 24.0% versus 66.5% for those patients with ALC ≥1.5 k/mm3 (p = 0.016). ALC remained a statistically significant predictor for OS when controlled for stage (HR = 0.4, p = 0.02), chemotherapy (HR = 0.38, p = 0.03), and gender (HR = 0.38, p = 0.04). ALC is a simple, easy to evaluate laboratory value that independently impacts prognosis for patients diagnosed with MCC when utilizing a cut point of <1.5 k/mm3. This test, already commonly obtained during the workup of patients with MCC, provides additional prognostic information to clinicians and patients with MCC.