(P 195) MULTIPLE MYXOMA EFFECTIVELY TREATED WITH PAZOPANIB - A CASE REPORT

Objective: Benign mesenchymal tumors rarely need medical treatment, but there may be cases where such tumors give rise to severe symptoms but are not possible to remove by surgery because of advanced growth adjacent to vital organs or multiplicity. Such a case is described here focusing on the different methods tried to alleviate severe and disabling symptoms in a seemingly unique condition. Several methods and drugs failed, but finally a treatment attempt was made with the tyrosine kinase inhibitor pazopanib, which has a demonstrated effect in several cases of soft tissue sarcomas. The slow but steady effect of this treatment may be of interest for other rare cases of benign but not operable mesenchymal tumors.

Methods: A 44-year old woman noticed a nodule on her left thigh in March 2009. Some months later similar nodules were noticed in the groins on each side. An MRI showed multiple intramuscular tumors, also at other locations. Excisional biopsy was performed from two of the lesions showing intramuscular myxoma without any signs of malignancy. With time, several tumors were growing giving rise to pain, gait difficulties, and sick leave. In September 2010, surgical removal was performed of two of the largest lesions, but fast re-growth did occur postoperatively. In May 2011, radiotherapy was used against one lesion in the right thigh with a transient effect of about one month. It was decided to start experimental medical therapy, and with no earlier reports in the literature of a similar condition, we tried in order, anti-estrogenic therapy with toremifen, mTOR-inhibition with everolimus, and interferon, before starting TKI treatment with pazopanib. At start of the last therapy, she had 14 measurable lesions of up to 30 cm in length.

Results: No, or only very limited, effects were registered after toremifen, everolimus, and interferon. After start of pazopanib no further progress was seen, and after three months some of the lesions became softer. After 8 months a marked regression of all lesions was found, the largest now measuring 22 cm, and only 5 were still measurable. One year after start the largest was only 12 cm, and 3 months later there was no measurable lesion left. MRI verified an almost complete regression. Some side effects encouraged us to a slow stepwise dose decrease during several months, but when we finally stopped treatment completely, a regrowth was obvious in several sites. Retreatment, however, led to a repeated extremely good effect, and the patient has now been on low doses of pazopanib during more than ten years, between 200 and 400 mg daily, which has been well tolerated and without occurrence of any worrying long-time side effects.

Conclusion: This rare case of multiple intramuscular myxomas demonstrates that VEGF-directed TKI, e.g., pazopanib, may be an excellent treatment modality also in benign mesenchymal tumors.