Response to Pham et al., “More data are needed to confirm the utility of screening for atypical fibroxanthoma and pleomorphic dermal sarcoma recurrence”
Authors: Mathias Ørholt, Frank Eriksson, Mikkel Herly, Peter Vester-Glowinski
Journal: Journal of the American Academy of Dermatology (2024)

To the Editor: We thank Pham et al1Pham J.P. Staeger R. Frew J.W. Response to Ørholt et al—more data are needed to confirm the utility of screening for atypical fibroxanthoma and pleomorphic dermal sarcoma recurrence.J Am Acad Dermatol. 2024; 90: e171-e173Abstract Full Text Full Text PDF PubMed Scopus (1) Google Scholar for their interest in our study on patients with atypical fibroxanthoma (AFX) and pleomorphic dermal sarcoma (PDS),2Ørholt M. Abebe K. Rasmussen L.E. et al.Atypical fibroxanthoma and pleomorphic dermal sarcoma: local recurrence and metastasis in a nationwide population-based cohort of 1118 patients.J Am Acad Dermatol. 2023; 89: 1177-1184https://doi.org/10.1016/j.jaad.2023.08.050Abstract Full Text Full Text PDF PubMed Scopus (5) Google Scholar and we appreciate the opportunity to discuss and clarify our analysis further. Pham et al1Pham J.P. Staeger R. Frew J.W. Response to Ørholt et al—more data are needed to confirm the utility of screening for atypical fibroxanthoma and pleomorphic dermal sarcoma recurrence.J Am Acad Dermatol. 2024; 90: e171-e173Abstract Full Text Full Text PDF PubMed Scopus (1) Google Scholar suggest that differences in follow-up length between patients with AFX and those with PDS may bias the detected differences between the groups. In our study, we estimated the risks of local recurrence and metastasis using the Aalen–Johansen estimator, which has been specifically developed to allow drawing of valid conclusions on a completely observed population based on observations with incomplete follow-up due to censoring.3Aalen O. Borgan O. Gjessing H. Survival and Event History Analysis: A Process Point of View. Springer Science+Business Media, 2008Crossref Google Scholar,4Overgaard M. Hansen S.N. On the assumption of independent right censoring.Scand J Stat. 2021; 48: 1234-1255https://doi.org/10.1111/sjos.12487Crossref Scopus (2) Google Scholar The Aalen–Johansen estimator does not require the same censoring distributions across groups but relies on the censoring being independent (ie, the rate of events in censored patients is not different from that in uncensored patients at any time within the same group).4Overgaard M. Hansen S.N. On the assumption of independent right censoring.Scand J Stat. 2021; 48: 1234-1255https://doi.org/10.1111/sjos.12487Crossref Scopus (2) Google Scholar The assumption of independent censoring is reasonable in our study because censoring is either due to migration or end of follow-up, which is not assumed to be related to the patients' future risk. We agree with Pham et al1Pham J.P. Staeger R. Frew J.W. Response to Ørholt et al—more data are needed to confirm the utility of screening for atypical fibroxanthoma and pleomorphic dermal sarcoma recurrence.J Am Acad Dermatol. 2024; 90: e171-e173Abstract Full Text Full Text PDF PubMed Scopus (1) Google Scholar that the 10-year risk of metastasis in patients without an event in the first 2 years seems higher in patients with PDS. However, this difference should be interpreted with caution owing to few events. We suggest different follow-up regimens for AFX and PDS because only 8 of 945 patients with AFX developed metastasis, resulting in a 10-year risk of metastasis of <1%. Routine PET/CT scans of patients with AFX would result in a high number of scans with a very low detection rate where costs, resources, and radiation dosage seem to outweigh the benefits. However, in patients with PDS, we believe that PET/CT should be a routine part of the follow-up program because there still is a 5-year risk of metastasis of 4.4% (95% CI, 0.2-8.7) if no metastasis occurs in the first 2 years after initial diagnosis (Fig 1). We believe that patients with PDS should be followed for at least 4 years, which is in accordance with European Society for Medical Oncology recommendations. However, as with all retrospective studies, we agree that the net benefit and cost effectiveness of such a follow-up program would benefit from a prospective validation. Pham et al1Pham J.P. Staeger R. Frew J.W. Response to Ørholt et al—more data are needed to confirm the utility of screening for atypical fibroxanthoma and pleomorphic dermal sarcoma recurrence.J Am Acad Dermatol. 2024; 90: e171-e173Abstract Full Text Full Text PDF PubMed Scopus (1) Google Scholar compare the overall survival in patients with metastatic PDS in our data set with that in a study conducted by Perez et al.5Perez A.N. Dashti N.K. Cates J.M.M. Prognostic factors for pleomorphic dermal sarcoma: analysis of 1911 cases from the SEER database.J Clin Pathol. 2023; 76: 424-428https://doi.org/10.1136/jcp-2022-208570Crossref PubMed Scopus (3) Google Scholar However, the numbers provided by Perez et al5Perez A.N. Dashti N.K. Cates J.M.M. Prognostic factors for pleomorphic dermal sarcoma: analysis of 1911 cases from the SEER database.J Clin Pathol. 2023; 76: 424-428https://doi.org/10.1136/jcp-2022-208570Crossref PubMed Scopus (3) Google Scholar are estimates of relative survival, which is a measure different from the crude overall survival reported in our study. The comparison is also challenged by small sample sizes because both studies report on fewer than 30 patients with metastatic PDS, resulting in wide CIs. Furthermore, in the study by Perez et al,5Perez A.N. Dashti N.K. Cates J.M.M. Prognostic factors for pleomorphic dermal sarcoma: analysis of 1911 cases from the SEER database.J Clin Pathol. 2023; 76: 424-428https://doi.org/10.1136/jcp-2022-208570Crossref PubMed Scopus (3) Google Scholar it was not possible to distinguish patients with AFX from those with PDS, and 65% of the patients had missing data regarding tumor growth depth, which was used as a surrogate marker for PDS. We therefore believe that comparisons of overall survival between the 2 studies are not possible. None disclosed. More data are needed to confirm the utility of screening for atypical fibroxanthoma and pleomorphic dermal sarcoma recurrenceJournal of the American Academy of DermatologyVol. 90Issue 5PreviewTo the Editor: We read with interest the retrospective nationwide analysis by Ørholt et al1 reporting on rates of local and metastatic recurrence for atypical fibroxanthoma (AFX) and pleomorphic dermal sarcoma (PDS) in Denmark. However, we wish to highlight aspects of their analysis limiting the strength of the proposed screening guidelines for patients with AFX and PDS. Full-Text PDF