Late Bone Metastasis of Histologically Bland Struma Ovarii: The Unpredictability of Its Biologic Behavior

Malignant Clinical Course of "Proliferative" Ovarian Struma: Diagnostic Challenges and Treatment Pitfalls

Struma ovarii (SO) is a monodermal teratoma predominantly composed of thyroid tissue (TT) showing benign, “proliferative”, or malignant histology. By imaging, a 38-year-old patient with lower backache revealed a 6.2-cm vertebral lesion (L5). Core biopsy showed well-differentiated TT without features of papillary carcinoma. A 3.5-cm left ovarian mature teratoma (lacking TT) and peritoneal nodules (showing well-differentiated TT) were also identified and surgically removed. Thyroid ultrasound and cytological examination resulted negative. Four years before, left ovarian cystectomy was performed for a histologically “proliferative” SO. According to the malignant clinical course and WHO classification, this case was overall reassessed as a recurring well-differentiated follicular carcinoma arising in SO (WD-FC-SO), despite lacking malignant histological features in any specimens. Immunophenotype: TTF-1+/PAX-8+/thyroglobulin+/CK7+/chromogranin-/synaptophysin-/inhibin-/calretinin-/HNF1B-; Ki-67 index < 5%. Polymerase chain reaction analysis resulted negative for BRAFV600E mutation. The patient refused further treatments, without recurrence after 17 months. The clinical behavior of SO may be unpredictable. Histologically benign or proliferative strumas extraordinarily metastasize, while SO with malignant features may not recur. The exceptional evidence of peritoneal implants of well-differentiated TT (peritoneal strumosis) in patients with histologically benign SO represents a metastasis of WD-FC-SO (like in our case). A multidisciplinary approach including clinical, laboratory, radiologic, and histopathological data is required.

Malignant struma ovarii with late recurrence harbouring high microsatellite instability

Struma ovarii (SO) is a rare ovarian teratoma containing abundant mature thyroid tissue. Malignant transformation is even less common and distant metastasis is documented in about 5%-10%. The time from diagnosis of primary SO to metastatic disease varies. As malignant SO is rare, there are no uniform diagnostic criteria or treatment guidelines. Management is usually extrapolated from that of thyroid malignancy. We report a patient who relapsed 12 years from the initial diagnosis and metastasised to the lungs 5 years after the first recurrence. Our patient was treated with total thyroidectomy followed by radioactive iodine, and retreated on progression in the lungs. The tumour harboured high microsatellite instability and treatment with programmed cell death protein 1 inhibitor was initiated. This case shows the long latency of SO with the rare phenomenon of metastasis. It also highlights the importance of molecular testing for rare cancers such as this.

Isolated Scapular Metastasis in a Patient with Malignant Struma Ovarii: A Case Report

CASE

We report the case of a 38-year-old woman who presented with a lytic bone lesion in the left scapula. A biopsy showed a tumor with the histologic appearance of thyroid tissue. She also was found to have a thyroid nodule and an enlarged ovary, both of which were excised. The thyroid nodule turned out to be a benign colloid nodule, and the ovary contained a monodermal teratoma composed of thyroid tissue (struma ovarii). The lesion in the scapula eventually was proven to be metastatic malignant struma ovarii.

CONCLUSION

Malignant struma ovarii with bone metastases is very rare, and its diagnosis is a challenge. There are some documented cases with bone metastases, mostly to the thoracic and lumbar spine. The optimal treatment of choice for the bone lesion is unknown because of the rarity of its presentation.