Identification of geographic clustering and regions spared by cutaneous T-cell lymphoma in Texas using 2 distinct cancer registries

Abstract

Background: Cutaneous T-cell lymphomas (CTCLs) (mycosis fungoides and its leukemic variant, Sezary syndrome) are rare malignancies. Reports of the occurrence of mycosis fungoides in married couples and families raise the possibility of an environmental trigger for this cancer. Although it has been suggested that CTCL arises from inappropriate T-cell stimulation, to the authors' knowledge no preventable trigger has been identified to date.

Methods: Using region, zip code, age, sex, and ethnicity, the authors analyzed the demographic data of 1047 patients from Texas who were seen in a CTCL clinic at The University of Texas MD Anderson Cancer Center during 2000 through 2012 (the MDACC database) and 1990 patients who were recorded in the population-based Texas Cancer Registry between 1996 and 2010. Subsequently, data from both databases were cross-analyzed and compared.

Results: The current study findings, based on the MDACC database, documented geographic clustering of patients in 3 communities within the Houston metropolitan area, in which CTCL incidence rates were 5 to 20 times higher than the expected population rate. Analysis of the Texas Cancer Registry database defined the CTCL population rate for the state to be 5.8 cases per million individuals per year (95% confidence interval, 5.5-6.0 per million individuals per year), thus confirming the observations from the MDACC database and further highlighting additional areas of geographic clustering and regions spared from CTCL in Texas.

Conclusions: The current study documented geographic clustering of CTCL cases in Texas and argued for the existence of yet unknown external causes/triggers for this rare malignancy.

Keywords: Sezary syndrome; cutaneous T-cell lymphoma (CTCL); disease hotspots; geographic clustering; mycosis fungoides; patient clustering.

Figure 1. Incidence of CTCL in Texas over time

Linear regression analysis of CTCL population incidence rate over time (R²=0.526, p=0.02). The slope of the line is 0.16 cases per million individuals per year (TCR database results).

Figure 2. Geographic distribution of CTCL in Texas (MDACC database results)

Geographic distribution of CTCL patients in the state of Texas based on zip code mapping analysis. Insets 1, 2 and 3 show incidence of disease in Dallas-Fort Worth, Austin-San Antonio and Houston metropolitan areas, respectively.

Figure 3. Detailed map of high CTCL incidence areas in Houston (MDACC database results)

Geographic mapping reveals CTCL high incidence areas, where patients with this rare cancer were residing along the same street/highway and/or streams. Patients in Spring are marked in violet, patients in Katy are marked in green, while patients residing in Houston Memorial area (zip code 77024) are marked in orange.

Figure 4. Geographic clustering of multiple high incidence zip codes across Texas (TCR Database Results)

Geographic distribution of CTCL high incidence zip code clusters (i.e., multiple high incidence zip codes located together) as indicated by blue squares and blue arrows for zip codes with total population >10,000 individuals. Inset 3 shows Houston Metropolitan area, where TCR analysis confirmed two out of three high incidence areas (Spring and Memorial area zip code 77024) as identified using the MDACC database and indicated with black arrows.