Primary Cutaneous Diffuse Large B Cell Lymphoma -Leg Type in United States: Epidemiology and Survival Outcome

Background: Primary cutaneous diffuse large B cell lymphoma-leg type (DLBCL-LT) is relatively uncommon lymphoma accounting for about 1 to 3 % of all cutaneous lymphoma and about 10-20% of primary cutaneous B cell lymphomas. There is data for survival outcomes in primary cutaneous B cell lymphoma in general population after introduction of rituximab but little is known about outcomes in DLBCL-LT patients in general population. The available data on survival in DLBCL-LT are from small case series and single institution studies. We conducted this study to evaluate the survival outcome in patients with PCDLBCL-LT after introduction of rituximab.

Methods: We utilized SEER 18 database to select adult (18+ years) patients diagnosed from 2004 to 2014 with ICD-3-0 code of 9680/3 (diffuse large B cell lymphoma, not otherwise specified)with localized stage by summary stage 2000 with skin as the primary site of disease to identify patient with DLBCL-LT. Patients were divided into various cohorts based on age (<65 versus 65+ years), sex, race (Caucasians, African American and Others) and median household income of county of residence (< $50,00 versus ≥ $50,000). We utilized SEER*stat to calculate age adjusted incidence rate using 2000 US standard population. Kaplan Meyer curve was utilized to calculate 5-year overall survival. Cox proportional hazard model was used for multivariate analysis of factor associated with survival.

Result: A total of 485 patients were identified with DLBCL-LT as the only or first primary cancer case. The median age at diagnosis was 70 years. Its incidence was found to be about 0.09 case per 100,000 population with incidence in males being about 1.6 times that of females. Majority of patient included in our study were males (52 %), older (59.4%), and Caucasians (85.6%). 5-year overall survival was found to be 59%. Older patients were found to have significantly worse 5-year overall survival compared to younger patients with HR of 7.9 with 95% CI of 4.9 to 12.7. There was no disparity in cancer outcome based on race, sex or median income of the county of residence. When we compared the outcome of patients diagnosed in earlier 5 years to later 6 years of the study period, the survival curves almost overlapped suggesting that there has been little if any improvement in outcome in recent years.

Conclusion: Our study showed that about 60% of patients with DLBCL-LT live for 5 years in real world setting which is comparable to the outcome reported by other studies on outcome in primary cutaneous B cell lymphoma. Even though this is disease of elderly, as the median age at diagnosis is 70 years, the outcome in older population was found to be significantly worse compared to younger patients. Given this is relatively uncommon disease, we recommend large registry-based studies to try to improve outcome in these patient population.