INCIDENCE OF SECOND PRIMARY MALIGNANCIES IN PATIENTS WITH SPORADIC DESMOID TUMORS

Introduction: Desmoid tumors (DT) account for approximately 0.03% of all neoplasms and fewer than 3% of all soft tissue tumors. Although locally aggressive and with a tendency for relapses, DT have no potential for metastasis or dedifferentiation. Most desmoids arise sporadically, and 5-15% of all cases are associated with familial adenomatous polyposis (FAP). However, the association of non-FAP DT with other second primary malignancies has not been adequately characterized. Objective: To investigate the incidence of second primary neoplasms in patients with DT not associated with FAP. Methods: A retrospective analysis was performed using the electronic database of a private hospital, including patients treated between Jan/2013 and May/2019. Eligibility criteria were: age of 18 years old or older and histologically confirmed desmoid tumor. Clinical characteristics and incidence of other primary tumors were evaluated. Patients with confirmed diagnosis of FAP were excluded. Results: A total of 34 patients diagnosed with DT were identified. FAP was present in 4 of these patients (11%). Among the non-FAP patients, 10 (33%) were male and 20 (64%) were female. The mean age of diagnosis was 37,9 yo (21-69 yo). Sites of presentation varied: abdominal wall in 33%, intra-abdominal in 16%, chest wall in 13,3%, paravertebral, breast and shoulder in 10% each, back and thigh in 3,3% each. Six (20%) patients had a second primary malignancy: 1 patient with GIST, 1 with colorectal cancer, 1 with testicular cancer, 2 with papillary thyroid cancer and 1 with melanoma. In 66% of these patients, the desmoid tumor was diagnosed before the second primary neoplasm, and all of these patients had undergone surgical treatment. Benign tumors such as neurofibroma and Erdheim Chester disease were identified in 2 patients. Somatic molecular analysis was performed in 6 patients and mutations in KIT, KRAS, MUTYH, MSH6, BRAF and POT1 were found. A second neoplasm was diagnosed in four of these six patients. Conclusion: Second primary neoplasms were present in 20% of our non-FAP desmoid tumors cohort. These data raise attention to the possibility of non-FAP hereditary conditions or shared risk factors, highlighting the need for close follow up of these patients.