Degree of differentiation of cutaneous squamous cell carcinoma: a comparison between a Swedish cohort of organ transplant recipients and immunocompetent patients

Background Organ transplant recipients (OTRs) have a very high risk of developing cutaneous squamous cell carcinoma (cSCC). Immunosuppressed OTRs may have a higher proportion of poorly differentiated cSCC than non-OTRs. Objectives The aim of this study was to investigate the degree of differentiation of cSCCs in OTRs compared with immunocompetent individuals. Patients/Methods Data from the Swedish Cancer Registry were crosschecked with data from the Transplant registry of the Transplant Institute at Sahlgrenska University Hospital in Gothenburg, Sweden. All OTRs with a diagnosis of cSCC, basosquamous carcinoma, and/or cSCC in situ established at the Department of Dermatology, Sahlgrenska University Hospital, during 2002–2015 were included. The control group consisted of non-OTRs with the same diagnoses during the same time period. Results During 2002–2015, 82 OTRs diagnosed with 515 tumors and 883 non-OTRs with 1,247 tumors were included. OTRs developed 0.47 tumors/year vs 0.10 tumors/year for non-OTRs, but no significant differences were observed in the degree of tumor differentiation of invasive cSCCs between OTRs and non-OTRs (P = 0.4). The distribution of poorly, moderately, and well-differentiated invasive cSCCs among OTRs and non-OTRs were 8.5% vs 12.5%, 22.1% vs 29.9%, and 69.4% vs 57.6%, respectively. Conclusions OTRs do not develop a higher proportion of poorly differentiated cSCCs than non-OTRs.


Introduction
Organ transplant recipients (OTRs) have a well-known increased risk of developing cancer due to immunosuppression [1]. Nonmelanoma skin cancer, particularly cutaneous squamous cell carcinoma (cSCC), is the most common malignancy seen in OTRs. Compared with the general population, the risk of developing cSCC is 60 to 100 times greater in OTRs [2][3][4]. Furthermore, cSCCs in OTRs have been shown to be more numerous and more aggressive compared with cSCCs in immunocompetent individuals [5][6][7]. In addition, the incidence of cSCC is proportional to the level of immunosuppression and is often associated with human papillomavirus (HPV) infection [8]. The pathogenesis of cSCC is multifactorial. For both OTRs and immunocompetent individuals, the most important risk factor for development of cSCC is UV radiation [9]. Fair skin is also seen as a risk factor [10]. There is a strong correlation between age and cSCC, with the highest incidence rates observed in men and women over 85 years of age [11]. Another risk factor for cSCC is the presence of oncogenic viruses in the skin [12]. In recent years, HPV has been associated with cSCC in OTRs. Among these patients, 80% of cSCCs are associated with HPV infection, in contrast to only 40% among immunocompetent individuals [13]. Greater age at transplantation as well as higher doses and longer duration of immunosuppressive regimens have also been identified as risk factors [9,14].
Histopathologically, cSCC originates from epidermal keratinocytes and consists of nests, sheets, and strands of epithelial cells that arise from the epidermis and invade into the dermis for a variable distance. The cSCCs are commonly divided into 3 categories: well differentiated, moderately differentiated, and poorly differentiated depending on the resemblance of the tissue of origin. There are no clear objective parameters for grading the differentiation of cSCCs [15], but one classification is that >75% of the cells are differentiated in well-differentiated tumors, 25%-75% in moderately differentiated tumors, and <25% in poorly differentiated tumors [7]. Well-differentiated cSCCs tend to grow at a slower rate and metastasize to a lesser extent than tumors that are poorly differentiated [16].

Results
: During 2002During -2015 OTRs diagnosed with 515 tumors and 883 non-OTRs with 1,247 tumors were included. OTRs developed 0.47 tumors/year vs 0.10 tumors/year for non-OTRs, but no significant differences were observed in the degree of tumor differentiation of invasive cSCCs between OTRs and non-OTRs (P = 0.4). The distribution of poorly, moderately, and well-differentiated invasive cSCCs among OTRs and non-OTRs were 8.5% vs 12.5%, 22.1% vs 29.9%, and 69.4% vs 57.6%, respectively.

Conclusions:
OTRs do not develop a higher proportion of poorly differentiated cSCCs than non-OTRs.

cSCC and cSCC In Situ
The tumor characteristics for both groups are presented in Table 2. The degrees of differentiation of the invasive cSCCs in OTRs compared with non-OTRs are shown in Figure 1.
In the OTR group, a total of 515 tumors were found with an average of 6.3 tumors/patient. The average follow-up time was 13.5 years, which corresponds to 0.47 tumors/year. Of the 515 tumors, 198 were cSCC in situ and 258 were cSCC with a known degree of differentiation. In these cases, 22 (8.5%) were poorly differentiated, 57 (22.1%) were moderately differentiated, and 179 (69.4%) were well differentiated.
The number of tumors in the non-OTR group was 1,247, an average of 1.4 tumors/patient and 0.10 tumors/year. Among these tumors, 86 were cSCC in situ and 1,019 were cSCC with a known degree of differentiation: 127 (12.5%) were poorly differentiated, 305 (29.9%) were moderately differentiated, and 587 (57.6%) were well differentiated. When comparing the distribution of the level of differentiation of the cSCCs with available data while also stratifying with respect to age group between the OTRs and non-OTRs, no significant difference was seen (P value 0.4, Mantel-Haenszel test).
As an incidental finding, an association was seen between the distribution of the level of differentiation of cSCCs and age groups below and above the median age at diagnosis in both groups. OTRs who were above the median age of 62 years had significantly fewer well-differentiated cSCCs (61%, CI 52-70) than younger OTRs (76%, CI 69-83) cSCC, moderately differentiated cSCC, poorly differentiated cSCC, and "cSCC, other" (including cases of invasive or microinvasive cSCC without a specified degree of differentiation, cSCC and basosquamous carcinoma). In some cases, the same tumor had several histopathological reports, eg, the first report was from a punch biopsy and the second report from when the tumor was excised in toto. In such cases, the lowest differentiation level was chosen, and the same tumor is represented only once in the material.

Statistical Analysis
All data were analyzed using R version 3.0. 3

Analysis of Study Population
Patient characteristics are shown in Table 1

Survival Analysis
The relative survival showed no difference between the 2 groups ( Figure 2). For non-OTRs, the relative survival was 0.84 (CI 0.78-0.89) and for OTRs it was 0.78 (CI 0.65-0.88).
There are several studies that show a more lethal and more aggressive behavior of cSCCs in OTRs [7,21]   infection, in contrast to only 40% among immunocompetent individuals [13].
With regard to the relative survival, no significant difference was seen between OTRs and non-OTRs, but the comparison is difficult to make due to the large difference in mean age between the groups.
A strength of this study is that the conditions for population studies in Sweden are ideal, thanks to a history of extensive record-keeping and the fact that each citizen is

Conclusions
There was no significant difference between the groups with regard to the proportion of poorly differentiated cSCCs. cSCCs (68.3%) [22]. In comparison with the non-OTRs, there was no significant difference in the degree of tumor differentiation. In fact, there was a slightly higher proportion of poorly differentiated cSCCs among non-OTRs (not significant).
As an incidental finding, we discovered that there was a higher frequency of poorly differentiated cSCCs in the to closer follow-up visits may also play a role among OTRs [23]. Notably, cSCC in situ was significantly more common in OTRs. This has also been seen in other studies [2,24]. NMSCs per person-year was 0.30 [2]. The higher number of tumors per person-year in our study may be explained by the fact that the study period was more recent and the incidence of cSCC in Sweden has increased during the past decade [25]. The patients in our study had also been immunosuppressed for a longer period of time (13.5 years vs 9.2 years).
Furthermore, the knowledge about the risk of cSCC in OTRs has increased and nowadays there is a much more organized system for follow-up visits which might have resulted in more diagnosed cases per patient.
Surprisingly, non-OTRs had a significantly higher proportion of tumors in the head and neck area compared with OTRs and the significance remained when comparing the anatomic location of the tumors between the groups for cSCCs and cSCC in situ lesions separately. All patients who undergo transplantation at SUH receive information about the risks of sun exposure. A hypothesis may be that OTRs therefore use sunscreen on the chronically exposed facial skin more frequently than non-OTRs. Another explanation could be that UV radiation is not the only risk factor for cSCCs in OTRs. In OTRs, 80% of cSCCs are associated with HPV