Background and Objectives: Carcinoma showing thymus-like differentiation (CASTLE) is a low-grade thyroid carcinoma, with an indolent clinical course and usually a favorable prognosis. The clinical and imagistic features are not specific for CASTLE but similar to other malignant lesions of the thyroid. Definite diagnosis is based on an immunohistochemical examination, as this carcinoma shows positive CD5 immunoreactivity when compared to other aggressive thyroid carcinomas. Case presentation: The main focus of this study is to outline a rare case of CASTLE compressing the trachea in a 50-year-old female patient who was initially diagnosed with undifferentiated thyroid carcinoma, for which she underwent unsuccessful surgery, as well as postoperative radiotherapy and chemotherapy. After receiving a second medical opinion, the patient underwent a challenging radical resection consisting in total thyroidectomy and central neck dissection, with no local recurrence after 6 months and 2 years of follow-up and negative metastatic follow-up. The correct diagnosis has been established based on pathological and immunohistochemical examinations. Conclusions: In summary, the diagnosis of CASTLE is difficult and requires an experienced histological analysis and CD5 immunoreactivity. Lack of metastasis, complete removal of the tumor, and a low degree of tumor infiltration into nearby structures are all associated with better long-term survival.

Parathyroid carcinoma (PC) is a rare and aggressive cancer affecting the parathyroid glands, presenting diagnostic and therapeutic challenges due to its rarity and overlapping features with benign parathyroid disease. This report describes the case of a 51-year-old patient with significantly elevated serum calcium levels, leading to further investigation. Imaging studies revealed a large nodular mass in the right inferior parathyroid gland. After undergoing right inferior parathyroidectomy, pathology confirmed parathyroid carcinoma. However, the patient experienced a relapse, detected via a neck MRI. This case highlights the importance of specific clinical features, such as rapid calcium increase, elevated parathyroid hormone (PTH) levels, and a large nodular mass, in suspecting malignancy. Differential diagnosis between carcinoma and adenoma can be challenging, and immunohistochemistry aids in diagnosis. Regular follow-up with calcium and PTH monitoring is essential for detecting recurrence. This case underscores the aggressive nature of parathyroid carcinoma and the importance of early diagnosis, surgical intervention, and thorough follow-up care for improved outcomes.

Acromegaly is associated with a higher risk of certain malignancies, but not hematological neoplasia, although multiple myeloma (MM) was found in very limited cases. We aim to present such a case, adding a particular presentation with co-occurrence of a plasmocytoma. A 52-year-old male with acromegaly confirmed at 46 (MRI: pituitary macroadenoma of 12 × 11 × 10 mm) underwent hypophysectomy followed by 3 years of octreotide LAR then lanreotide depot. After another 6 months, he experienced a rapidly growing, painful lump in the right lateral thoracic area confirmed by CT as a 9-cm osteolytic lesion at the third rib. Core biopsy revealed plasmocytoma of the bone and medullary biopsy confirmed MM. Plasmacytoma was managed with 10 radiotherapy sessions, with favorable outcome and mass resorption; MM was managed with a VRD regimen, followed by autologous hematopoietic stem-cell transplantation. Six months after sFLC normalization and plasmacytoma resorption, complete remission was reported. In the meantime, lanreotide was continued, with complete acromegaly control. To conclude, what started as a rather typical scenario for an otherwise rare condition, as is acromegaly in the general population (but not so rare for endocrinologists), turned into an unexpected and more severe outcome. Noting this exceptional association, we pinpoint that further research is needed for understanding the dual acromegaly–MM relationship.