Tumor-induced osteomalacia (TIO) is a rare disorder of phosphate wasting due to fibroblast growth factor-23 (FGF23)-secreting tumors that are often difficult to locate. We present a systematic approach to tumor localization and postoperative biochemical changes in 31 subjects with TIO. All had failed either initial localization, or relocalization (in case of recurrence or metastases) at outside institutions. Functional imaging with 111 Indium-octreotide with single photon emission computed tomography (octreo-SPECT or SPECT/CT), and 18 fluorodeoxyglucose positron emission tomography/CT (FDG-PET/CT) were performed, followed by anatomic imaging (CT, MRI). Selective venous sampling (VS) was performed when multiple suspicious lesions were identified or high surgical risk was a concern. Tumors were localized in 20 of 31 subjects (64.5%). Nineteen of 20 subjects underwent octreo-SPECT imaging, and 16 of 20 FDG-PET/CT imaging. Eighteen of 19 (95%) were positive on octreo-SPECT, and 14 of 16 (88%) on FDG-PET/CT. Twelve of 20 subjects underwent VS; 10 of 12 (83%) were positive. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were as follows: sensitivity ¼ 0.95, specificity ¼ 0.64, PPV ¼ 0.82, and NPV ¼ 0.88 for octreo-SPECT; sensitivity ¼ 0.88, specificity ¼ 0.36, PPV ¼ 0.62, and NPV ¼ 0.50 for FDG-PET/CT. Fifteen subjects had their tumor resected at our institution, and were disease-free at last follow-up. Serum phosphorus returned to normal in all subjects within 1 to 5 days. In 10 subjects who were followed for at least 7 days postoperatively, intact FGF23 (iFGF23) decreased to near undetectable within hours and returned to the normal range within 5 days. C-terminal FGF23 (cFGF23) decreased immediately but remained elevated, yielding a markedly elevated cFGF23/iFGF23 ratio. Serum 1, (1,25D) rose and exceeded the normal range. In this systematic approach to tumor localization in TIO, octreo-SPECT was more sensitive and specific, but in many cases FDG-PET/CT was complementary. VS can discriminate between multiple suspicious lesions and increase certainty prior to surgery. Sustained elevations in cFGF23 and 1,25D were observed, suggesting novel regulation of FGF23 processing and 1,25D generation.

Pathologically elevated serum levels of fibroblast growth factor-23 (FGF23), a bone-derived hormone that regulates phosphorus homeostasis, result in renal phosphate wasting and lead to rickets or osteomalacia. Rarely, elevated serum FGF23 levels are found in association with mosaic cutaneous disorders that affect large proportions of the skin and appear in patterns corresponding to the migration of ectodermal progenitors. The cause and source of elevated serum FGF23 is unknown. In those conditions, such as epidermal and large congenital melanocytic nevi, skin lesions are variably associated with other abnormalities in the eye, brain and vasculature. The wide distribution of involved tissues and the appearance of multiple segmental skin and bone lesions suggest that these conditions result from early embryonic somatic mutations. We report five such cases with elevated serum FGF23 and bone lesions, four with large epidermal nevi and one with a giant congenital melanocytic nevus. Exome sequencing of blood and affected skin tissue identified somatic activating mutations of HRAS or NRAS in each case without recurrent secondary mutation, and we further found that the same mutation is present in dysplastic bone. Our finding of somatic activating RAS mutation in bone, the endogenous source of FGF23, provides the first evidence that elevated serum FGF23 levels, hypophosphatemia and osteomalacia are associated with pathologic Ras activation and may provide insight in the heretofore limited understanding of the regulation of FGF23.

Context COVID-19 is a major health problem because of saturation of intensive care units (ICU) and mortality. Vitamin D has emerged as a potential treatment able to reduce the disease severity. Objective To elucidate the effect of calcifediol [25OHD3] treatment on COVID-19-related outcomes. Design Observational cohort study from March to May, 2020. Setting Patients admitted to COVID-19 wards of Hospital del Mar, Barcelona, Spain. Patients A total of 930 patients with COVID-19 were included. Ninety-two were excluded due to previous calcifediol intake. Intervention Of the remaining 838, a total of 447 received calcifediol (532ug on day one plus 266ug on day 3, 7, 15, and 30) whereas 391 were not treated at the time of hospital admission (Intention-to-Treat). Of the latter, 53 patients were treated later during ICU admission and were allocated in the treated group in a second analysis. In healthy subjects, calcifediol is about 3.2-fold more potent on a weight basis than cholecalciferol. Main Outcome Measures ICU admission and mortality. Results ICU assistance was required by 102 (12.2%) participants. Out of 447 patients treated with calcifediol at admission, 20 (4.5%) required ICU, compared to 82 (21%) out of 391 non-treated (p-value<0.0001). Logistic regression of calcifediol treatment on ICU admission, adjusted by age, gender, linearized 25OHD levels at baseline, and comorbidities showed that treated patients had a reduced risk to require ICU (OR 0.13 [95% CI 0.07;0.23]). Overall mortality was 10%. In the Intention-to-Treat analysis, 21 (4.7%) out of 447 patients treated with calcifediol at admission died compared to 62 patients (15.9%) out of 391 non-treated (p=0.0001). Adjusted results showed a reduced mortality risk with an OR 0.21 [95% CI 0.10; 0.43]). In the second analysis, the obtained OR was 0.52 [95% CI 0.27;0.99]. Conclusions In patients hospitalized with COVID-19, calcifediol treatment significantly reduced ICU admission and mortality.