# Radiation Oncology/Sarcoma/DFSP

* Front Page: Radiation Oncology | RTOG Trials | Randomized Trials
Dermatofibrosarcoma Protuberans

## Epidemiology

* Cutaneous, locally aggressive, primarily low grade sarcoma
** ~10% may contain a high-grade fibrosarcoma component
** Low rate (<5%) of metastasis; higher if fibrosarcoma component
* Rare, 2-6% of soft tissue sarcomas
* Adults in 30's
* Risk factors: pregnancy, arsenic exposure, acanthosis nigricans

## Clinical Presentation

* Plaque-like areas of cutaneous thickening
* Skin-colored, red-brown, or violaceous, particularly at the margins
* May arise within pre-existing scar or tattoo
* As it slowly enlarges, becomes raised ("protuberans"), firm, and nodular (fixed to dermis, but moves over deeper structures)
** At diagnosis, >75% are superficial and <5cm diameter
* Slow, indolent growth, such that the lesion may be present for years
* Distribution:
** Trunk ~50%
** Lower extremity ~20%
** Upper extremity 15%
** Head and neck 15%

## Work Up

* MRI helpful to estimate extent of deep extent
* CT not routinely necessary, unless bony invasion suspected
* Metastatic workup not routinely necessary, unless suspicion from H&P

## Histology

* Cell of origina is not well understood
** Histochemistry and electron microscopy suggest fibroblast lineage
** However, the cells are CD34 positive, suggesting possibly dendritic lineage
** In comparison, dermatofibromas and desmoid tumors are CD34-
* The tumors show benign-appearing spindle cells, in an irregular patterns resembling a straw mat. In early lesions there is a tumor-free zone with epidermis
* >90% have a t(17;22) translocation, resulting in a fusion of PDFG-B driven by a highly expressed collagen promoter (COL1A1)
** Results in PDFGRb activation, which is tyrosine kinase receptor

## Staging

* AJCC 7th Edition (2010)
** First edition to include DFSP
** Please see the Soft Tissue Sarcoma staging page
* American Musculoskeletal Tumor Society Staging for DFSP
** Stage IA - Low or intermediate grade within the subcutaneous compartment
** Stage IB - Low or intermediate grade extending outside anatomic compartment
** Stage II - High grade histology

## Natural History

* Tends to recur locally after excision alone
* Recur locally multiple times before metastasis; significant interval before development of metastases.
* Fibrosarcomatous changes predict for metastatic potential.

## Treatment Overview

* Surgical resection is the primary treatment approach
** Historically, wide local excision with 3cm margins was recommended, down to and including fascia
** Mohs mapping reveals fine tentacles of tumor, and is becoming favored due to preservation of cosmesis
** Some recommend modified Mohs to include a final path margin for permanent section
** Pooled local recurrence rate with adequate margin WLE or Mohs' is <2%
** Recurrences tend to occur within 3 years of surgery
* Definitive RT not routinely; only couple reports available
* Adjuvant radiation is typically indicated if positive or close margins, further resection anatomically not possible if recurrence happens, or recurrent disease
* Given the high rate of t(17;22) leading downstream to a tyrosine kinase activation, efforts are under way to use Gleevec and other TKIs in this disease

### Adjuvant Radiation Therapy

* MD Anderson
** 2013 (1972-2010) PMID 23628134 -- Dermatofibrosarcoma Protuberans: Long-term Outcomes of 53 Patients Treated With Conservative Surgery and Radiation Therapy. (Castle KO, Int J Radiat Oncol Biol Phys. 2013 Jul 1;86(3):585-90. doi: 10.1016/j.ijrobp.2013.02.024. Epub 2013 Apr 26.)
*** Retrospective. 53 consecutive patients. Surgery and preoperative (13%) or postoperative (87%) RT. Median tumor size 4 cm (1-25 cm). Preop dose 50 Gy, postop dose 60-66 Gy. Gross disease 7%, positive margin 30%. Median F/U 6.5 years
*** Outcome: Recurrence 4%. 5-year and 10-year OS 98%. Fibrosarcomatous change not associated with risk of LR or DM
*** Toxicity: 13%; moderate/severe complications 9% at 10 years
*** Conclusion: DFSP is radioresponse with excellent local control after surgery and RT. Adjuvant RT should be considered if large/recurrent tumor or where attempt at wide surgical margins would result in significant morbidity
** 1998 PMID 9531366 -- "The role of radiation therapy in the management of dermatofibrosarcoma protuberans." (Ball MT, Int J Radiat Oncol Biol Phys. 1998 Mar 1;40(4):823-7.
*** Retrospective. 19 patients receiving adjuvant xrt. 60 Gy given for +microscopic margin; 65 Gy given for gross residual disease. Local control at 10 yrs was 95%
*** Conclusion: adjuvant xrt should be considered for +margins or if adequate wide excision would lead to major cosmetic defect.
* Soft Tissue Tumours Working Group, The Netherlands Cancer Institute; 1997 PMID 9376187 -- Haas RL et al. "The role of radiotherapy in the local management of dermatofibrosarcoma protuberans."
** 38 consecutive pts w/ DFSP. 21 tx'd surgically, 17 tx'd w/ combined modality.
** Surgery alone had local control of 67%
** Combined modality had local control of 82% (many of these who had xrt already had multiple local recurrences.
* Harvard; 1996 PMID 8708729 -- Suit H et al. "Radiation in management of patients with dermatofibrosarcoma protuberans." J Clin Oncol. 1996 Aug;14(8):2365-9.
** 18 patients treated with postop (n=15) or definitive (n=3) xrt. Population was +/close margins or xrt alone.
** Local control at 10yrs was 88%.