Abstract

Background: Increasing incidence rates of soft tissue sarcomas (STS) have been reported. In the present study, the authors have analyzed the incidence of STS in Austria in a population-based study for the period 1984–2004.

Patients and methods: Age-adjusted incidence rates, gender and age predilection and geographic differences were analyzed, comprising data from the Austrian National Cancer Registry.

Results: A total of 5333 cases were registered; male-to-female ratio was 0.8. The most common histotypes were sarcoma not otherwise specified (36%), leiomyosarcoma (24%), liposarcoma (12%), malignant fibrous histiocytoma (9%) and fibrosarcoma (5%). Age-adjusted incidence rate was 2.4 per 100 000 per year. Analysis of annual incidence rates and 3-year periods showed no increase (annual increasing gradient = −0.0025).

Conclusions: This study has analyzed the most recent data from a European population in comparison with seven international studies. An increase, as postulated elsewhere, could not be confirmed. The incidence rate of STS in Austria ranges in the lower half of the international incidence rates (1.8–5.0 per 100 000 per year). Different inclusion criteria (Kaposi's sarcoma and dermatofibrosarcoma) and classifications in the various studies explain the increase of incidence in some studies rather than true increase of STS due to new or accumulated risk factors.

introduction

Soft tissue sarcomas (STS) are a rare group of tumors, arising from mesenchymal tissue with heterogeneous differentiation. They account for ∼1% of all malignancies [1, 2]. Little is known about the etiology of STS. Only for a small part of all cases, specific risk factors, like radiation and herbicides, containing chlorophenol and phenoxy acids [3–7], have been identified. These findings, however, are not supported by other studies [8]. Hereditary syndromes, such as Li–Fraumeni and Werner syndromes, and possible unidentified syndromes [9] seem to be associated with another small percentage of all STS cases.

International incidence rates range between 1.8 and 5.0 cases per 100 000 per year [2, 10–14]. Increasing incidence rates of STS have been reported by several authors [2, 11, 14, 15]. This trend is assumed to be caused by increasing rates of acquired immunodeficiency syndrome (AIDS)-related Kaposi's sarcoma [2] or increasing exposure to radiation or herbicides [15, 16] or to be the result of recent shifts in the diagnostic criteria and classification of STS [14].

Gender predilection is varying in different nations and studies [10–12, 15]. Furthermore, Smola et al. [17] have postulated diversity in the incidence rates of the different provinces in Austria.

The aim of the present study was to analyze the trends in the incidence of STS in Austria from 1984 to 2004 and to take into closer examination the different factors mentioned above.

patients and methods

The authors have carried out a retrospective, population-based analysis of the incidence of STS in Austria and a literature review concerning incidence, as well as gender and age predilection. Patients with STS were identified using data from the Austrian National Cancer Registry for the period from 1984 to 2004. The collected information includes general demographic characteristics of the patients (age, sex and province of residence), site and histotype of the tumor according to the standard International Classification of Diseases for Oncology, third revision (ICD-O-3) [1] and the year of diagnosis confirmation. Included were all cases that met the morphologic criteria of STS following the Blue Book classification of the International Agency for Research on Cancer (IARC) [1], regardless of primary site, except bones and joints, as proposed by the World Health Organization (WHO) guidelines.

The Austrian National Cancer Registry covers the whole population of Austria, ∼8.3 million (2007) inhabitants. All patients with STS in Austria are registered in the Austrian National Cancer Registry. It is located in Vienna and operated by Statistics Austria since 1969. The Austrian 1969 Cancer Statistics Act and the 1978 Cancer Statistics Ordinance provide the statutory basis for the Austrian Cancer Registry and oblige hospitals to report every cancer case to Statistics Austria.

The duty of notification allows running a population-based registry for the whole Austrian population. Hospitals fill in a form providing information about the tumor (topography, histology and behavior of the tumor and incidence date) as well as general personal and demographic information of the patients (age, sex and province of residence). The stage of the tumor at diagnosis and the first treatment are also reported. All invasive and in situ tumors are registered, and topography, morphology and behavior are coded according to ICD-O-3.

All incoming data are stored in a database that carries out data checks at the point of data entry. These plausibility checks are based on the IARC-CHECK program, broadened at national level. IARC rules for classifying multiple primaries are implemented as well. Multiple notifications for the same person are identified using the full name, date of birth, sex and address as well as Social Security number. For the quality control and assessment of completeness, electronic data of pathology laboratories and of various study groups are used.

The causes of death statistics are used for passive follow-up and for generating the death certificate-notified (DCN) cases. These DCN cases have died of cancer (according to the death certificate) but have not yet been reported as incidence cases to Statistics Austria. Statistics Austria follows the IARC's recommendation and traces them back, if the patients died in a hospital, to obtain the complete information. Cases that cannot be researched are considered as death certificate-only (DCO) cases. The resulting DCO rate can be consulted as a completeness indicator of the registry. Since 1997, the Austrian DCO rate has been constantly <10%, which is the IARC-recommended threshold for good quality data.

Since 2003, the Austrian Cancer Registry has been considered as a dynamic database since it allows constant updating of all former years. To publish a new report year, a snapshot of the database is frozen, which forms the basis for further analysis until the publication of the new report year.

Age-adjusted incidence rates were calculated using the population data for each age group and year obtained from Statistics Austria and the WHO world standard population of 2001 for each age group. Male-to-female ratio, age predilection and the regional distinctions in the different provinces were analyzed.

results

age-adjusted incidence rate

The age-adjusted incidence rate of STS in Austria was 2.4 per 100 000 individuals per year (Figure 1) for the analyzed period from 1984 to 2004. The annual incidence rates ranged between 2.1 and 2.7 per 100 000 individuals. Analysis of trends in the incidence of STS in Austria did not show any significant rate of change over time (annual gradient = −0.0025). Likewise, analysis of 3-year periods did not reveal any significant trend concerning the reported increase of incidence rates (Figure 1).

Figure 1.

Age-adjusted incidence rates of soft tissue sarcomas for the years 1984–2004 in Austria.

Figure 1.

Age-adjusted incidence rates of soft tissue sarcomas for the years 1984–2004 in Austria.

distribution of histotypes

A total of 5333 cases of STS were found during the observed period of 21 years. Table 1 shows the distribution of all histotypes. The most common histotype was sarcoma not otherwise specified (1915 cases, 36%), followed by leiomyosarcoma (1268 cases, 24%), liposarcoma (652 cases, 12%), malignant fibrous histiocytoma (MFH) (506 cases, 9%) and fibrosarcoma (267 cases, 5%). Eighty-seven cases (2%) of Kaposi's sarcoma were found, the first cases of Kaposi's sarcoma having appeared in 1988, supporting the fact that Austria is not an endemic area of this neoplasm.

Table 1.

Distribution of histotypes of 5333 cases of STS in Austria (1984–2004)

Morphology code ICD-O-3 Histotype n (%) 
8800 Sarcoma NOS 1915 (35.91) 
8890 Leiomyosarcoma 1268 (23.78) 
8850–58 Liposarcoma 652 (12.23) 
8850 Liposarcoma NOS 482 
8852 Myxoid liposarcoma 87 
8854 Pleomorphic liposarcoma 39 
8851 Well-differentiated liposarcoma 29 
8855 Mixed-type liposarcoma 
8858 Dedifferentiated liposarcoma 
8853 Round cell liposarcoma 
8830 Malignant fibrous histiocytoma 506 (9.49) 
8810–14 Fibrosarcoma 267 (5.01) 
8810 Fibrosarcoma NOS 204 
8811 Low-grade fibromyxoid sarcoma, myxofibrosarcoma 61 
8814 Infantile fibrosarcoma 
9120 Angiosarcoma of soft tissue 253 (4.74) 
9040 Synovial sarcoma 119 (2.23) 
8901, 8910–20 Rhabdomyosarcoma 95 (1.78) 
8910 Embryonal rhabdomyosarcoma 56 
8920 Alveolar rhabdomyosarcoma 28 
8901 Pleomorphic rhabdomyosarcoma 11 
9140 Kaposi's sarcoma 87 (1.63) 
8990 Malignant mesenchymoma 59 (1.11) 
8804 Epithelioidsarcoma 41 (0.77) 
9364 Primitive neuroectodermal tumor 25 (0.47) 
9581 Alveolar soft part sarcoma 18 (0.34) 
9044 Clear cell sarcoma of soft tissue 14 (0.26) 
9240 Mesenchymal chondrosarcoma 10 (0.19) 
8963 Extrarenal rhabdoid tumor 3 (0.06) 
9133 Epithelioid haemangioendothelioma 1 (0.02) 
Morphology code ICD-O-3 Histotype n (%) 
8800 Sarcoma NOS 1915 (35.91) 
8890 Leiomyosarcoma 1268 (23.78) 
8850–58 Liposarcoma 652 (12.23) 
8850 Liposarcoma NOS 482 
8852 Myxoid liposarcoma 87 
8854 Pleomorphic liposarcoma 39 
8851 Well-differentiated liposarcoma 29 
8855 Mixed-type liposarcoma 
8858 Dedifferentiated liposarcoma 
8853 Round cell liposarcoma 
8830 Malignant fibrous histiocytoma 506 (9.49) 
8810–14 Fibrosarcoma 267 (5.01) 
8810 Fibrosarcoma NOS 204 
8811 Low-grade fibromyxoid sarcoma, myxofibrosarcoma 61 
8814 Infantile fibrosarcoma 
9120 Angiosarcoma of soft tissue 253 (4.74) 
9040 Synovial sarcoma 119 (2.23) 
8901, 8910–20 Rhabdomyosarcoma 95 (1.78) 
8910 Embryonal rhabdomyosarcoma 56 
8920 Alveolar rhabdomyosarcoma 28 
8901 Pleomorphic rhabdomyosarcoma 11 
9140 Kaposi's sarcoma 87 (1.63) 
8990 Malignant mesenchymoma 59 (1.11) 
8804 Epithelioidsarcoma 41 (0.77) 
9364 Primitive neuroectodermal tumor 25 (0.47) 
9581 Alveolar soft part sarcoma 18 (0.34) 
9044 Clear cell sarcoma of soft tissue 14 (0.26) 
9240 Mesenchymal chondrosarcoma 10 (0.19) 
8963 Extrarenal rhabdoid tumor 3 (0.06) 
9133 Epithelioid haemangioendothelioma 1 (0.02) 

STS, soft tissue sarcomas; ICD-O-3, International Classification of Diseases for Oncology, third revision; NOS, not otherwise specified.

localization of the tumor

The main part of all 5333 cases (3312 cases, 62%) is coded as tumor of mesothelial and soft tissue (C45–C49), including the localizations upper and lower extremity, trunk, retroperitoneum and peripheral nerves, among others (Table 2), not distinguishing between each subcategory. The other two main localizations of STS are female genital system (702 cases, 13%) and digestive system (605 cases, 11%). According to their histopathologic characteristics, uterus sarcoma (ICD-O-3 code: 8494) and gastrointestinal stromal cancer (ICD-O-3 code: 8936) are not included in these data.

Table 2.

Localization of 5333 cases of STS in Austria (1984–2004)

ICD-O-3-code Topographic distribution n (%) 
C00–C14 Oral cavity and pharynx 50 (0.94) 
C15–C26 Digestive system 605 (11.34) 
C30–C39 Respiratory system and other intrathoracal organs 172 (3.23) 
C45–C49 Mesothelial and soft tissue 3312 (62.10) 
C45 Mesothelioma  
C46 Kaposi's sarcoma  
C47 Peripheral nerve and visceral nervous system  
C48 Retroperitoneum and peritoneum  
C49 Connective tissue, subcutaneous tissue and other soft tissue  
C49.0 of head, face and neck  
C49.1 of upper extremity and shoulder  
C49.2 of lower extremity and hip  
C49.3 of thorax  
C49.4 of abdomen  
C49.5 of pelvis  
C49.6 of trunk NOS  
C49.8 of overlapping sites  
C50 Breast 138 (2.59) 
C51–C58 Female genital system 702 (13.16) 
C60–C63 Male genital system 80 (1.50) 
C64–C68 Urinary system 157 (2.94) 
C69–C72 Eye and orbit, brain and central nervous system 44 (0.83) 
C73–C75 Thyroid and other endocrine system 69 (1.29) 
C76–C80 Miscellaneous 4 (0.08) 
ICD-O-3-code Topographic distribution n (%) 
C00–C14 Oral cavity and pharynx 50 (0.94) 
C15–C26 Digestive system 605 (11.34) 
C30–C39 Respiratory system and other intrathoracal organs 172 (3.23) 
C45–C49 Mesothelial and soft tissue 3312 (62.10) 
C45 Mesothelioma  
C46 Kaposi's sarcoma  
C47 Peripheral nerve and visceral nervous system  
C48 Retroperitoneum and peritoneum  
C49 Connective tissue, subcutaneous tissue and other soft tissue  
C49.0 of head, face and neck  
C49.1 of upper extremity and shoulder  
C49.2 of lower extremity and hip  
C49.3 of thorax  
C49.4 of abdomen  
C49.5 of pelvis  
C49.6 of trunk NOS  
C49.8 of overlapping sites  
C50 Breast 138 (2.59) 
C51–C58 Female genital system 702 (13.16) 
C60–C63 Male genital system 80 (1.50) 
C64–C68 Urinary system 157 (2.94) 
C69–C72 Eye and orbit, brain and central nervous system 44 (0.83) 
C73–C75 Thyroid and other endocrine system 69 (1.29) 
C76–C80 Miscellaneous 4 (0.08) 

Topographic distribution of 5333 cases of STS in Austria from 1984 to 2004.

STS, soft tissue sarcomas; ICD-O-3, International Classification of Diseases for Oncology, third revision; NOS, not otherwise specified.

age and gender predilection

Analysis of age distribution showed a peak incidence of STS around the age of 60 years (Figure 2) and a second, modest peak in early childhood (0–5 years). The age predilection reveals that STS in general are malignancies of the advanced age except for the remarkable peak in the period between 0 and 5 years of age.

Figure 2.

Age distribution of soft tissue sarcomas incidence for the years 1984–2004 in Austria.

Figure 2.

Age distribution of soft tissue sarcomas incidence for the years 1984–2004 in Austria.

For the observed period, the male-to-female ratio was 0.8 (2317 males and 3016 females). The male-to-female ratio showed a broad range over the years with a ratio between 0.56 (in 1988) and a nearly outbalanced male-to-female ratio of 0.98 (in 2003).

province of residence

Slightly differing incidence rates could be seen for the different provinces of Austria. The incidence rates of the different provinces ranged between 2.1 and 3.2 per 100 000 per year. The highest incidence rate was found in Tyrol (3.2 per 100 000 per year) and the lowest in Carinthia (2.1 per 100 000 per year), Burgenland and Styria (2.2 per 100 000 per year). The incidence rates of the remaining provinces, Vienna, Lower and Upper Austria, Burgenland and Salzburg, ranged between 2.3 and 2.7 per 100 000 per year (Figure 3).

Figure 3.

Incidence rates of soft tissue sarcomas in the different provinces of Austria for the period 1984–2004.

Figure 3.

Incidence rates of soft tissue sarcomas in the different provinces of Austria for the period 1984–2004.

When analyzing these results, one must be aware of the small total numbers of STS cases for each single province, which can result in a high variability of incidence rates. In Salzburg, for example, the age-adjusted incidence rate ranged between minimum 0.9 and maximum 4.1 per 100 000 per year and in Vorarlberg, between minimum 0.7 and maximum 4.4 per 100 000 per year, with no consistent trend in any direction.

discussion

age-adjusted incidence rate

The Austrian age-adjusted incidence rate of STS of 2.4 per 100 000 per year ranges within the elsewhere-calculated incidence rates between 1.8 and 5.0 per 100 000 per year [2, 10–15]. When comparing the results of different nations, one must take into account the differences of inclusion criteria, the small absolute numbers of cases of STS and the possible different classification and typing standards for each country and time period.

The incidence in Austria is lower than the reported incidence rates of the United States [2, 14], Denmark [10], The Netherlands [11] and Switzerland [12] (Table 3) but higher than the incidence rate reported from Sweden, with 1.8 per 100 000 per year [13]. The Swedish data, however, include only patients >16 years and STS of the extremities and the trunk wall, whereas all other studies, including this one, comprised all patients regardless of age and all STS regardless of primary site.

Table 3.

Trends in incidence of STS, summary of reviewed literature concerning observed period, incidence, trends and gender predilection

Author (nation) Observed period Incidence rate (per 100 000 per year) Increasing incidence of STS Gender predilection male/female 
Gustafson (Sweden) 1964–1989 1.8 n.s. n.s. 
Levi (Switzerland) 1974–1994 3.6 Noa 0.88 
Storm (Denmark) 1948–1987 3.2 Noa >1 
Ross (United States)b 1973–1987 4.4 Noa 0.93 
Zahm (United States) 1935–1989 4.0 Yesa 1.42 
Toro (United States)b 1978–2001 5.0 Yesa >1 
Schuurman (The Netherlands) 1950–1988 4.7 Yesc 1.17 
This study (Austria) 1984–2004 2.4 Noc 0.8 
Author (nation) Observed period Incidence rate (per 100 000 per year) Increasing incidence of STS Gender predilection male/female 
Gustafson (Sweden) 1964–1989 1.8 n.s. n.s. 
Levi (Switzerland) 1974–1994 3.6 Noa 0.88 
Storm (Denmark) 1948–1987 3.2 Noa >1 
Ross (United States)b 1973–1987 4.4 Noa 0.93 
Zahm (United States) 1935–1989 4.0 Yesa 1.42 
Toro (United States)b 1978–2001 5.0 Yesa >1 
Schuurman (The Netherlands) 1950–1988 4.7 Yesc 1.17 
This study (Austria) 1984–2004 2.4 Noc 0.8 
a

Kaposi's sarcoma excluded.

b

Caucasian population.

c

Kaposi's sarcoma included.

STS, soft tissue sarcomas; n.s., not specified.

Results from the United States show a higher incidence in the Afro-American population than in the Caucasian population [2, 14], and Storm [10] points out the different incidence rates for the Maori population, New Zealand [representative for Oceania people (native islanders)], and for the Osaka population, Japan (Asian population). But even when comparing the results of the Caucasian population in the United States with the present study, higher incidence rates can be seen in the United States.

The studies from the United States used the Surveillance, Epidemiology and End Results (SEER) program as data source. The SEER program started in 1973. It covers ∼10% of the USA population, including the population-based cancer registries of nine states (CT, CA, HI, IA, KY, LA, NJ, NM and UT), several metropolitan areas (Detroit, San Francisco-Oakland Registry and Seattle-Pudget Sound Registry) and certain geographic areas to cover specific minority populations [Local tumor registries of Alaska Natives, Arizona Indians, Los Angeles and San Jose-Monterey (Hispanics) and Rural Georgia (Afro-Americans)]. The considerably higher rates in the United States compared with the other studies may partly be explained as Zahm [15] reasons, “it is usually possible to estimate the number of cancer cases expected to be diagnosed each year in the country. For STS however, the SEER program may overestimate the true national experience because it includes San Francisco Bay Area, which has very high rates of AIDS-related Kaposi's sarcoma”.

The results from Switzerland [12], neighboring country of Austria, show higher incidence rates for STS (3.6 per 100 000 per year) than the present study too. The Swiss data were extracted from the Cancer Registry of the Canton of Vaud. Situated in Western Switzerland, Vaud covers 8.8% of the Swiss population. The period from 1974 to 1994 was analyzed and a total of 645 cases were found. The Swedish data are based on a local registry as well: the Regional Musculoskeletal Tumor Center, University Hospital, Lund, Sweden [13]. Only this study and the study from Denmark [10] have analyzed data of nationwide cancer registries. The data from Denmark reach back to 1943, indicating the long history of tumor registration in this country.

Closer analysis of the data sources of the different studies reveals different inclusion criteria (Table 4). This study and the study from Sweden [13] exclude dermatofibrosarcoma (ICD-O-3: 8832/3, WHO Tumors of Skin, C44.9), according to the WHO guidelines for coding STS [1]. The studies from The Netherlands and the United States [2, 11, 14], on the other hand, included dermatofibrosarcoma into their dataset. Dermatofibrosarcoma accounts for 6.2%–9.5% of all STS in these collectives (Table 4), and these studies show notably higher incidence rates for STS than the present study and the study from Sweden (Table 3).

Table 4.

Most common histotypes of STS in different nations

Histotype Distribution of the most common histological subtypes in total number and (%)
 
This study, Austria Gustafson, Sweden Levi, Switzerland Schuurman, The Netherlands Ross, United States Toro, United States 
Total number of cases 5333 508 645 1992 18 525 26 758 
Sarcoma, NOS 1915 (36) 29 (6) 49 (7.6) 87 (4.4) 999 (5.4) 3208 (12.0) 
Leiomyosarcoma 1268 (24) 66 (13) 164 (25.4) 400 (20.1) 3280 (17.7) 5873 (23.9) 
Liposarcoma 652 (12) 53 (10) 55 (8.5) 274 (13.8) 1016 (5.5) 2879 (11.5) 
MFHa 506 (9) 209 (41) n.s. 323 (16.2) 1855 (10.0) 4283 (17.1) 
Fibrosarcoma 267 (5) 16 (3) 124 (19.2) 114 (5.7) 703 (3.8) 878 (3.3) 
Kaposi's sarcoma 87 (2) – 101 (15.7) 277 (13.9) 3122 (16.9) – 
Synovial sarcoma 119 (2) 36 (7) 15 (2.3) 40 (2.0) 267 (0.1) n.s. 
Dermatofibrosarcoma –b –b n.s. 179 (8.9) 1152 (6.2) 2535 (9.5) 
Histotype Distribution of the most common histological subtypes in total number and (%)
 
This study, Austria Gustafson, Sweden Levi, Switzerland Schuurman, The Netherlands Ross, United States Toro, United States 
Total number of cases 5333 508 645 1992 18 525 26 758 
Sarcoma, NOS 1915 (36) 29 (6) 49 (7.6) 87 (4.4) 999 (5.4) 3208 (12.0) 
Leiomyosarcoma 1268 (24) 66 (13) 164 (25.4) 400 (20.1) 3280 (17.7) 5873 (23.9) 
Liposarcoma 652 (12) 53 (10) 55 (8.5) 274 (13.8) 1016 (5.5) 2879 (11.5) 
MFHa 506 (9) 209 (41) n.s. 323 (16.2) 1855 (10.0) 4283 (17.1) 
Fibrosarcoma 267 (5) 16 (3) 124 (19.2) 114 (5.7) 703 (3.8) 878 (3.3) 
Kaposi's sarcoma 87 (2) – 101 (15.7) 277 (13.9) 3122 (16.9) – 
Synovial sarcoma 119 (2) 36 (7) 15 (2.3) 40 (2.0) 267 (0.1) n.s. 
Dermatofibrosarcoma –b –b n.s. 179 (8.9) 1152 (6.2) 2535 (9.5) 
a

Malignant fibrous histiosarcoma.

b

Dermatofibrosarcoma (ICD: 8832/3) not registered, according to the WHO guidelines for coding STS.

STS, soft tissue sarcomas; NOS, not otherwise specified; MFH, malignant fibrous histiocytoma; n.s., not specified; ICD, International Classification of Diseases; WHO, World Health Organization.

Still, the true incidence of STS remains uncertain to some degree. Underreporting of these malignancies is one problem, as well as the changing of classification over time. In order to keep this error source as small as possible, the authors have analyzed data from the Austrian National Cancer Registry, which contains the collected cases from every hospital in Austria. Thereby, we were able to investigate the most updated and complete data source available. As mentioned before, Statistics Austria minimizes the problem of underreporting by working with the concept of a dynamic database. With a DCO rate <10%, the Austrian National Cancer Registry is regarded a provider for good quality data.

Analysis over a longer period of time includes different classification and typing systems and may thus produce inconsistent numbers. In 1990, Statistics Austria adopted the system of the four-digit code for morphologies following the ICD. All cases from former years have automatically been reinterpreted. Hence, the morphological criteria chosen for this study have been the same for all report years considered.

The reported increase of STS in the United States and The Netherlands [2, 11, 14, 15] cannot be confirmed by our data (Table 3). Note that Schuurman et al. [11] (The Netherlands) did not exclude Kaposi's sarcoma, which counts for 13.9% of all STS in that collective (compared with only 2% Kaposi's sarcoma in Austria). Ross et al. [2] stated that when excluding Kaposi's sarcoma, the incidence rates remained relatively unchanged throughout the observed time period. These findings, concluding no increase of STS, are supported by studies from Switzerland and Denmark [2, 10, 12] and the present study.

distribution of histotypes

The differences in the distribution of histotypes in the various studies [2, 11–14] have been analyzed, showing nonuniform results (Table 4). Leiomyosarcoma is the prevailing subgroup in all studies and nations; the distribution of the remaining entities shows no homogeneity. Not even Switzerland and Austria show matching distributions, in spite of being neighboring countries, situated in the Alps, with comparable environmental factors.

Inherent classifications and histopathologic differentiation are some of the factors which render the interpretation of geographic variety difficult [10, 15].

As mentioned before, different inclusion criteria for dermatofibrosarcoma can be seen in the different studies. Changing of classification over time is another factor which may lead to differing distributions of histotypes. For example, the concept of MFH has evolved since the upcoming of immunochemistry [1]. Formerly, the pleomorphic type of MFH has been regarded as the prototypical form of MFH and the most common histotype in adults. The results of the study from Sweden by Gustafson [13], where the observed period ends in 1989, reflect this historical definition (Tables 3 and 4). Nowadays, the former group of MFH is divided into a wide variety of poorly differentiated neoplasms, the main histotypes being pleomorphic sarcoma (synonym: pleomorphic malignant fibrous histiosarcoma, MFH pleomorphic type) and myxofibrosarcoma (synonym: myxoid malignant fibrous histiosarcoma, MFH myxoid type). In consequence, analysis of more recent data shows lower incidence rates for MFH (Tables 3 and 4).

localization of the tumor

In view of clinical aspects, a more detailed differentiation of the tumor site seems preferable, in order to analyze differences in various parameters, such as the date of definite diagnosis of the tumor, time of first symptoms or prognosis, depending on the tumor localization. Incidence rates for specific tumor sites could then be analyzed, as part of an epidemiologic analysis. In accordance with other epidemiologic studies [2,10–12, 14, 15], the present study divided the tumor sites into more crude categories.

age and gender predilection

The age distribution in Austria with two peaks of incidence, one minor in early childhood and a major peak around the age of 60 years, is in line with the age distribution determined in previous studies [12], where rhabdomyosarcoma is the dominant histotype in the age group between 0 and 5 years [9, 14, 15].

International comparison of gender predilection for STS reveals diverse findings (Table 3). Higher incidence of STS in females, as found in Austria, are reported for Switzerland too [12]. In the United States, the two studies of Ross et al. [2] and Toro et al. [14] present different male-to-female ratios, even though both studies have comprised their dataset from the SEER program. Thus, with this inconsistency in the results from the different studies, no clear tendency in the gender predilection can be stated, and drawing conclusions concerning the causation of these findings seems unreasonable.

province of residence

Although Austria is a small country (83 871 km2), there are varying types of landscapes. Austria is a largely mountainous country (Central Eastern Alps, Northern Limestone Alps and Southern Limestone Alps), only 32% of the country lie <500 m (1640 ft) and only a quarter can be considered low lying (Vienna basin, Pannonian low country and the foothills of the Alps). Therefore, the authors have investigated possible differences in incidence rates of STS for the different provinces. Analysis showed differing incidence rates in the different provinces but not consistently correlated to the sea level of the provinces. The highest incidence rate was found in Tyrol (3.2 per 100 000 per year), which is part of the alpine regions; the lowest incidence rates were found in Vorarlberg and Carinthia (2.3 and 2.1 per 100 000 per year, respectively), although these two provinces belong to the mountainous landscape as well.

The interpretation of these differences is to be done with caution due to the small absolute numbers of STS in each province. In addition, one has to consider that the different provinces have different registration standards. Tyrol, Carinthia, Salzburg and Vorarlberg have local cancer registries and send the collected data to the Austrian National Cancer Registry, whereas the other provinces report the cancer cases directly from the hospital to Statistics Austria. The local cancer registry in Tyrol, for example, is researching every case of DCN, where it is possible, and thereby produces DCO rates constantly <1%. Compared with the nationwide standard of <10%, the high quality of the local Tyrolean Cancer Registry might explain the higher incidence rates in this province. Thus, different incidence rates may be the result of differing levels of completeness of the registration in each province rather than differences in the incidence itself.

conclusions

The elsewhere-observed increasing trend in the incidence of STS could not be confirmed by the results of the present study, which analyzed the incidence of STS in Austria for the period from 1984 to 2004. The incidence rate for STS with 2.4 per 100 000 per year lies in the lower half of the international incidence rates (1.8–5.0 per 100 000 per year). Differing inclusion criteria in the published literature for both Kaposi's sarcoma and dermatofibrosarcoma could be seen. These findings in combination with increasing rates of AIDS-related Kaposi's sarcoma may explain the elsewhere-reported increase of incidence of STS rather than true increase of STS due to new or accumulated risk factors.

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