Purpose. The relevance of the initial observational approach for desmoid tumors (DTs) remains unclear. We investigated a new conservative management treatment for primary abdominal wall DTs. Methods. Data were collected from 147 patients between 1993 and 2012. The initial therapeutic approaches were categorized as front-line surgery [surgery group (SG), n = 41, 28 %] and initial observation or medical treatment [nonsurgery group (NSG), n = 106, 72 %]. The cumulative incidence of the last strategy modification was estimated using competing risk methods with variable censoring times. Results. Of the 147 patients, 143 were female (97 %). In the SG, 27 patients (66 %) required full-thickness abdominal wall mesh repair. In the NSG, 102 patients (96 %) underwent initial observation and four received medical treatment. In the NSG, the 1- and 3-year incidences of changing to medical treatment (no further changes during the follow-up) were 19 % [95 % confidence interval (CI) 11-28] and 25 % (95 % CI 17-35), respectively, and the 1- and 3-year incidences of a final switch to surgery were 14 % (95 % CI 8-22) and 16 % (95 % CI 9-24), respectively. An initial tumor size of [7 cm was associated with a higher strategy modification risk (p = 0.004). Of the 102 patients initially observed, 29 experienced spontaneous regression over a median followup period of 32 months. All second-intent resections were macroscopically completed, with R0 resections achieved in 82 % of patients. Conclusions. This study supports an initial nonsurgical approach to abdominal wall DTs B7 cm, followed by surgery based on tumor growth in select cases.
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