A single-institutional review of 68 patients with dermatofibrosarcoma protuberans: wide re-excision after inadequate previous surgery results in a high rate of local control

The rarity of DFSP and the low number of recurrence events pose epidemiological challenges and preclude even large studies to assess the prognostic factors of RFS. Dermatofibrosarcoma protuberans can lead to significant morbidity due to its aggressive local growth and the high rates of local recurrence despite surgical resection. In the present study, 15.4% of all R0 resected patients developed a local recurrence during the course of the disease. The two largest, well-characterized studies from the Instituto Nazionale Tumori (INT) and the Memorial Sloan-Kettering Cancer Center (MSKCC) presented cohorts with local recurrence rates of 4.3 and 22.1%, respectively [4, 5]. The distinct variation between those two studies reflects the differences in tumour histology, as the INT series contained a lower percentage (3.2%) of patients with the more aggressive FS-DFSP subtype than the MSKCC series (17%). In the present study, a relatively high proportion of patients (20.6%) had a FS-DFSP, which was found to be one of the most significant adverse predictors of RFS in our study. Hence, the observation of high recurrence rates is probably due to differences in patient selection and the corresponding tumour pathology between the two institutions reported and our institution.

Incomplete resections in the form of “whoops” procedures are common in the previous history of DFSP patients. A total of 79.2% of all patients referred came to our institution after incomplete resections. However, further re-excision led to negative margins in nearly all cases, except for three patients. It is notable that pathologic residual disease could be detected in 85.5% of the re-excised patients. In our series, re-excision to achieve wide, clear margins has been determined to be an effective method of achieving a high rate of local control in patients who presented after R1 or marginal R0 resection. This finding provides a liberal policy of re-excision after inadequate surgery.

It is interesting that re-excision appeared to be a significant predictor of RFS when analysed as a potential prognostic event. The reason, therefore, might lie in the fact that re-excision led to wider negative margins. The margin width attained surgically was a statistically significant predictor of the outcome in the univariate and the regression analysis in the subgroup analysis of 48 patients with negative margins. None of the patients with negative margins above 1 cm had a local recurrence during follow-up. Accordingly, a surgical margin width of 1 cm was a cutoff point in our series. However, this was the histologically assessed margin width in the pathologic specimen, and we cannot conclude which safety margins planned preoperatively are needed in order to obtain a histologically clear margin of 1 cm. Hence, the recommended lateral safety margins ranging from 2 to 3 cm might be justified in most of the cases localized at the trunk or proximal extremities, whenever feasible [7, 10, 23, 27, 28].

A high need for reconstructive procedures was observed in our patient population (47.1%) as a consequence of wide and radical re-excisions. Reconstructive procedures had to be performed in 30.2, 30.3 and 72.2% of all patients treated in other institutions that did not use MMS [3, 5, 8]. It is notable that the highest rate was reported by a plastic surgical department, presumably due to a selection bias. This observation might also give the impression that plastic surgeons are more inclined to perform reconstructive procedures when they are also responsible for tumour resection. However, these retrospective observations cannot be used to evaluate the treatment approaches of the different disciplines involved. The use of reconstructive surgery in our series displayed an improved outcome in univariate analysis, but this distribution failed to reach statistical significance in multivariate analysis, because the use of reconstructive surgery was associated with a larger margin width. The median negative surgical margin width was 0.5 cm for primary closed wounds and 1.3 cm for wounds with plastic surgical tissue transfer. The reason, therefore, might be a selection bias where wider resections necessitated the use of reconstructive surgery more frequently. Vice versa, plastic surgical tissue transfer enabled wider resections due to the safe wound coverage and, therefore, might have led to more radical resections.

Only three patients received adjuvant radiation in our series. Thus, we cannot make any reliable conclusions regarding the efficacy of adjuvant radiotherapy. Nevertheless, adjuvant radiotherapy remains a treatment option for tumours that only can be resected with close or positive surgical margins in critical anatomic sites [5, 30]. Radiation can also be used as an exclusive treatment option in locally advanced tumours where further surgery is not possible [31]. A retrospective study by the MD Anderson Cancer Center analysed the outcome of 53 DFSP patients treated with pre- or postoperative radiation and presented a local control rate of 98% after 5 years [32]. The authors recommended adjuvant radiation for patients with large or recurrent tumours or when surgical attempts at wide margins would result in significant morbidity. Finally, the question remains whether adjuvant radiotherapy should be applied in patients with FS-DFSP despite negative margins. To date, there are no studies that have analysed the prognostic effects of radiation on both DFSP subtypes separately. Hence, there are no clear suggestions whether radiation should be applied generally in patients with R0-resected FS-DFSP.

There are no randomized controlled studies to date comparing MMS and WLE, but MMS seems to result in significantly lower local recurrence rates [3, 19‐22]. Mohs micrographic surgery should be preferred particularly in the treatment of head and neck lesions, because it allows greater preservation of normal tissue, resulting in a better functional and aesthetic outcome [33]. Although superior to WLE, MMS has some limitations when large or subfascial tumours at the trunk or the distal extremities are involved [3]. However, the current series is not able to comment on the use of MMS, because there were no patients in our database who were treated with MMS, either in our or the referring institutions. Despite consistent reports about the advantages of MMS, it is still not a common procedure in German clinical routine [15].

Finally, the intervals of follow-up care should be addressed so that recurrences can be detected at an early disease stage. Unfortunately, the other centres did not delineate their follow-up strategies. The German guidelines recommend clinical examinations only every 6 months during the first 5 years but state explicitly that reliable data do not exist [34]. In the present study, the mean time to local recurrence was 9 months in patients in whom local recurrence occurred. However, we were not able to assess the median time to local recurrence because of the low number of recurrence events. The recent MSKCC series with 159 patients reported a medium time to local recurrence of 32 months [6]. Therefore, intense follow-ups during the first 5 years seem reasonable. The last recurrence in our series occurred after two and a half years. This observation raises the question whether a follow-up up to 5 years might be adequate for patients with DFSP or should continue even after 5 years. In contrast to our study, the INT and MSKCC also reported late recurrences that developed more than 5 years after primary diagnosis. However, because of the small number of events after 5 years, we cannot conclude whether follow-up examinations are necessary after this long time period. The follow-up management for DFSP in our institution includes clinical examinations and contrast-enhanced MRIs every 3 months in the first 2 years and then every 6 months for three more years. The decision whether follow-up MRIs should be continued after 5 years for every 6 or 12 months is based on the previous tumour behaviour and the decision of the informed patient. Finally, we have to state that this follow-up strategy is only based on our own experiences with a small proportion of patients suffering late recurrences and is not supported by any data of high evidence.