Changes in Nonmelanoma Skin Cancer Incidence between 1977–1978 and 1998–1999 in Northcentral New Mexico¹

NMSC³ is a highly common form of malignancy in light-skinned populations. In the United States alone, an estimated 1 million cases of cutaneous BCC and SCC are newly diagnosed each year, mostly in non-Hispanic whites (1). Unlike other forms of cancer, population-based surveillance of NMSC is not conducted in the United States, mainly because of the many annual cases, most of which are diagnosed and treated in dermatology offices and clinics rather than hospitals. Absent routine surveillance, measuring NMSC incidence requires special population-based surveys of physician and clinic records to identify and collect the requisite data on incident cases. The United States National Cancer Institute sponsored several such surveys in 1971–1972 (2) and 1977–1978 (3), the results of which showed marked geographic variation in NMSC incidence; the highest rates occurring in those areas with the highest levels of ambient solar UV radiation. Subsequent surveys from other populations in North America (4, 5, 6, 7, 8), Australia (9), and Europe (10, 11, 12), all suggest substantial increases in NMSC incidence have occurred since the 1970s.

The NMTR, a statewide population-based cancer registry and original member of the National Cancer Institute Surveillance, Epidemiology, and End Results Program, participated in the 1977–1978 national skin cancer survey by ascertaining newly diagnosed cases of NMSC among the resident population of New Mexico. Incidence rates in New Mexico non-Hispanic whites were among the highest of the eight geographic areas covered in the survey, which included the standard metropolitan statistical areas of Minneapolis-St. Paul, San Francisco-Oakland, Detroit, and Atlanta, the King County area of Seattle, metropolitan New Orleans, and the entire states of Utah and New Mexico. To examine temporal patterns of change in the occurrence of NMSC within the high incidence area of New Mexico, we recently undertook a 20-year follow-up survey of skin cancer among state residents using protocols used in the 1977–1978 survey. We report here BCC and SCC incidence rate data for non-Hispanic white residents of a three-county area in northcentral New Mexico for two 12-month time periods June 1, 1977 to May 31, 1978 and July 1, 1998 to June 31, 1999.

The same protocol used in the 1977–1978 New Mexico skin cancer survey was used to identify and collect data on state residents who developed at least one independent, primary malignant NMSC during the 1998–1999 survey period. As in our earlier survey, we accessed the records of all in-state pathology laboratories, dermatologists, and dermatopathologists, as well as those of other select physicians known by NMTR to diagnose or treat skin cancer (e.g., plastic surgeons, radiologists, general surgeons). Bordering out-of-state regions were not included in the catchment area for either survey. Trained NMTR staff visited practice sites across the state to identify newly diagnosed NMSCs (histological or clinical diagnosis) and abstract patient demographic and medical data. Tumors diagnosed as a recurrence or metastases from a previously treated tumor were not considered new primaries and were excluded. A standard abstract form was used to collect demographic and medical information, including personal identifiers, age, sex, race/ethnicity, residence address at diagnosis, date of diagnosis, and tumor histology and location. County of residence at diagnosis was derived from patient address at diagnosis. Race/ethnicity was assigned by established registry procedures that use charted information in the medical record.

For analysis, age-adjusted and age-specific incidence rates of newly diagnosed BCC (International Classification of Disease–Oncology: Morphology: 8090–8093) and SCC (International Classification of Disease–Oncology: Morphology: 8070–8076) in non-Hispanic white residents of Bernalillo, Sandoval, and Santa Fe counties were calculated according to gender and anatomical site using original source data from the 1977–1978 and 1998–1999 surveys. These three largely suburban counties are located in northcentral New Mexico, share contiguous borders, and historically account for ∼40% of the total state population. In addition, they harbor a substantial portion of the state’s medical resources and facilities, including dermatologists and pathology laboratories, and are each situated at considerable distance (>70 miles) from the state border. Land elevation of the population centers in the three county area ranges from 5000 to 7000 feet above sea level.

Incidence rates for each time period were based on people, counting each person only once, regardless of the number of newly diagnosed skin cancers reported. Those people diagnosed with both BCC and SCC lesions were included in the SCC counts only. Population denominators for the 1977–1978 rate calculations were obtained as 5-year age-, gender-, and racial/ethnic-specific county estimates from the NMTR population data archive, generated as described previously (13). Corresponding population denominators for the 1998–1999 data were obtained as annual population estimates directly from the United States Census. All age-adjusted rates were directly standardized to the 2000 United States standard population using 5-year age groups. SEs for rates were estimated based on the normal approximation to the Poisson distribution.

A total of 4194 cases of newly diagnosed NMSC (3103 BCCs and 1091 SCCs) was identified in non-Hispanic white residents of Bernalillo, Sandoval, and Santa Fe counties in New Mexico during the 12-month time period July 1, 1998 to June 30, 1999. During the earlier 1977–1978 survey, we identified a total of 1387 incident NMSC cases (1121 BCCs and 266 SCCs). In either time period, >98% of the lesions diagnosed were based on histological confirmation. The age-adjusted incidence of BCC in males increased by 50% between the two surveys from 618.7/100,000 in 1977–1978 to 930.0/100,000 in 1998–1999 (Table 1). In comparison, the age-adjusted incidence of BCC in females rose by 21% from 398 to 485/100,000. For SCC, age-adjusted incidence rates increased by 90% in males from 187 to 356/100,000 and by 109% in females from 71 to 150/100,000. The percentage change in both BCC and SCC crude rates increased with advancing age in males, the effect being most striking for SCC, where a modest temporal decline in rates among men ages 25–54 years was offset by a strong increase in rates among those ages ≥ 55 years. No corresponding age effect was observed in females; a marginal decline in BCC crude rates occurred in women ages 45–64 years compared with a marginal increase at other ages, whereas for SCC, strong temporal increases in crude rates occurred across all age groups.

Table 2 provides age-adjusted BCC and SCC incidence rates according to major anatomical site. During both survey periods, BCC incidence rates were highest for the head and neck, accounting for ∼75% of the overall incidence in both males and females. BCC rates were next highest for the trunk, followed by the upper limb and lower limb, again regardless of sex and survey period. Temporal increases in BCC rates occurred at each anatomical site. In males, a modest increase in the rate of BCC on the head and neck (34%) and lower limbs (27%) contrasted with strong increases in rates for the trunk (168%) and the upper limbs (418%). Among females, strong temporal increases in the rate of BCC on the upper limbs (276%) and lower limbs (231%) contrasted with a modest increase for the trunk (88%) and a marginal change for the head and neck (6%).

For SCC, incidence rates were highest for the head and neck, followed by the upper limb, then the trunk and lower limb, regardless of sex and survey period. As with BCC, the SCC incidence rates increased over time at each anatomical site. For males, the largest percentage rate increase occurred at the lower limbs (463%) and upper limbs (269%), followed by the trunk (118%) and the head and neck (59%). A similar pattern was observed in females, where the percentage change in SCC incidence was greatest for the lower (397%) and upper (132%) limbs, followed by the head and neck (95%) and trunk (29%).

Our findings indicate that between 1977–1978 and 1998–1999, the incidence of NMSC in the non-Hispanic white population of northcentral New Mexico approximately doubled for SCC, whereas that for BCC increased by ∼50% in males and 20% in females. As we had access to the records of all area pathology laboratories and dermatologists in the catchment area and used the same active case ascertainment method, there is little reason to believe the increased incidence measured in 1998–1999 is because of enhanced casefinding. We also believe our rates reflect essentially complete case ascertainment because the incidence data were obtained from larger state-based surveys, both of which effectively allowed the geographic range of casefinding for the three-county analysis area to be extended up to the state borders. In addition, because the analysis was limited to a region geographically removed from the state’s border, there is little reason to believe that cases were missed in either time period because of out of state diagnosis or treatment.

Other factors potentially could have accounted for the observed increase in NMSC rates, including heightened public awareness of skin cancer, leading to more lesions being brought to medical attention, as well as changes in physician practice toward enhanced detection and removal of lesions. Although we have no data to directly evaluate such effects, we believe them to be minimal. Our finding that NMSC rates declined in various gender and age groups over time, particularly BCC in middle-aged women, would not be consistent with increased detection alone accounting for the higher rates in 1988–1989. Similarly, the age-dependent changes in BCC and SCC rates we observed in males, but which were absent in females, would argue against a generalized detection effect, as would the markedly different pattern of temporal change we observed for rates of BCC (i.e., 6%) and SCC (i.e., 95%) on the head and neck of females.

If our findings reflect a true underlying increase in the occurrence of NMSC, the measured doubling of SCC rates is of particular concern because this histological type is relatively aggressive and causes the majority of NMSC deaths. In this regard, however, it is important to emphasize that our results are limited to two time periods separated by roughly two decades. In the absence of intervening data points, we have no way of determining the actual shape of the SCC or BCC incidence curve over this broad time frame. Recently published data from a population-based skin cancer registry in southeastern Arizona, a geographic area in close proximity to New Mexico, suggest that rates of SCC may have actually peaked in the mid-1980s and are now in decline (8). A similar finding was reported for skin cancer data collected up through 1998 in the Swiss Canton of Vaud (12), but other studies indicate that SCC rates have increased unabated over time up through the mid-1990s (6, 9, 10, 11). Continued surveillance of BCC and SCC is clearly warranted to better understand how incidence rates may be changing over time.