F-FDG18PET/CT incidental detection of tumor-to-tumor metastasis in patients investigated for squamous cell lung cancer

Abstract

Tumor-to-tumor metastasis (TTM) is a well-known entity, although this is still an extremely rare phenomenon. The lung cancers are considered the most frequent metastatic donors while kidney cancers are the most common recipient. The finding of TTM is often incidental during a biopsy of metastases or on surgical specimens but never suspected on radiological assessment of tumor extension. The finding of an unexpected region of Fluorodeoxyglucose (FDG) uptake can occur when performing whole body Positron Emission Tomography/computed tomography (PET/CT) scan and potentially raises the possibility of a second primary tumor. However, PET/CT scan incidental detection of tumor-to-tumor metastasis has never been reported in English literature. We report here a case of clear cell renal carcinoma, receptor of metastases originating from an oligometastatic squamous cell lung cancer detected on the PET/CT scan performed as part of the extension workup. Morphological and immunohistochemical analysis of a percutaneous biopsy of the renal mass were consistent with the diagnosis of a metastasis of lung cancer into renal cell carcinoma. This is the first case of oligometastatic lung cancer with the occurrence of TTM suspected in PET/CT scan. Although this is a rare setting, it should be considered in daily practice, as it could potentially modify the oncological management offered to the patients.

Keywords: FDG, Fluorodeoxyglucose; ISUP/WHO, International Society of Urologic Pathologists/world health organization; PET/CT detection; PET/CT, Positron Emission Tomography/ Computed Tomography; SUV, standardized uptake values; TTM, Tumor to tumor metastasis; Tumor-to-tumor metastasis.

Fig. 1A

A thoracic computed tomography scan showing an intra-parenchymal tumour process in the upper segment of the right lower lobe with hilar and right mediastinal lymph nodes. Figure 1B Abdominal CT revealed a polar mass in the left kidney.

Fig. 2

A and B PET/CT showed hypermetabolic mass of lower lobe (SUVmax of 9.8/large axis 63 mm) with ipsilateral mediastino-hilar and subcarinal metastatic lymph nodes (SUV max of 7.5). Figure 2C Inferior polar left renal mass of heterogeneous density and hypermetabolism measuring 8 cm in long axis with focal uptake on its superior-external side (SUVmax of 8). Figure 2D Inferior polar left renal mass of heterogeneous density and hypermetabolism measuring 8 cm in long axis with focal uptake on its superior-external side (SUVmax of 8).

Fig. 3A

Renal cell proliferation (right side of the image) associated with an epidermoid-like differentiating contingent (arrow on the left side of the image) HEx10. Figure 3B Intense nuclear expression of P40 only in the squamous differentiation contingent (x10). Figure 3C CD10 expression only in the renal cell contingent (x10).