Non-contrast CCT of a 56-year-old asymptomatic male patient who had been routinely followed up due to the diagnosis of laryngeal cancer for one year demonstrated a newly emerging hypodense solid mass on the left side of anterior thoracic wall at the level of second costae. The mass measured 25x35x37 mm in size caused destruction in the adjacent costa and invaded the pectoralis muscle (Figure 5a and 5b). There was also an extension of the mass to the intrathoracic area with pleural thickening and reticulations in the adjacent lung parenchyma, suggesting invasion (Figure 5c). Several lymph nodes, the largest of which was 8x7mm in size, were observed in the left internal mammary chain (Figure 5d). In 18F-FDG PET/CT performed for further evaluation, increased F-18 FDG uptake (SUVmax: 12.0) was noted in the lesion (Figure 5e). In the differential diagnosis of the lesion, laryngeal cancer metastasis, haematological malignancies, tuberculosis, soft tissue sarcoma and malignant pleural mass were considered. After an excisional biopsy, the diagnosis of the lesion was reported as IgG4-RRD.