Geographic variation of extranodal sites of mucosal associated lymphoid tissue lymphoma (MALToma): Analysis of series from two institutions.

Abstract

e18534 Background: MALToma represents about 5% of Non-Hodgkin lymphomas (NHL). Prior studies report stomach to be the most common site of involvement (35-50%), while skin (16%) or salivary glands (26%) were reported to be the 2nd most frequent site in 2 different studies. Geographical variation may affect the proportions of primary sites of MALToma, which could provide further clues to investigating their causes. Methods: The data was obtained on 91 consecutive patients from the University of Arizona Cancer Center (UACC) clinical and pathological databases, and 25 patients from the Cook County Hospital (CCH) database, seen between 2005 and 2011.The frequency of clinical characteristics and their relation to survival were analyzed and compared between UACC and CCH. Results: UACC and CCH cohorts were balanced for gender (M:F ratio 0.65) and age (median 63 y (range, 26-88), but not for race or/and ethnicity. While at CCH 36% of pts were African-American (AA), 28% Hispanic (any race), 12% Caucasian and 20% unknown; at UACC 88% of pts were Caucasian, 10% Hispanic and 1% AA (p<0.0001). UACC had 8% pts with > 1 extranodal site, while CCH had none. The primary sites of MALToma were also different. At CCH, similarly to what’s commonly reported in the literature, 40% of pts had primary gastric involvement, 20% salivary gland, 12% lung, 8% orbit, 8% thyroid, 4% intestine, 4% skull base tumor, and 4% breast. At UACC, however, 22% of pts had primary skin involvement, 19% gastric, 16% lung, 13% orbit, 8% salivary gland, 6% intestine, 5% breast, 3% thyroid and 8% other. The difference was statistically significant for the frequency of primary skin (p=0.006) but not gastric involvement (p=0.084). 80% of patients with primary skin involvement were Caucasian. The median follow-up of the survivors was 18 months for both groups, with no statistically significant difference in median progression-free (7.5 years) or overall survival (14.6 years). Conclusions: There was higher prevalence of Caucasian race and skin involvement at UACC than at CCH. We speculate that sun-induced photodamage causes chronic inflammation contributing to eventual malignant transformation to primary skin MALToma.