Complications related to thyroidectomy among patients with hyperthyroidism: Exploring the potential for ambulatory surgery

BACKGROUND

Total thyroidectomy for hyperthyroidism is typically followed by overnight admission to monitor for complications including thyrotoxicosis. Outpatient thyroid surgery is increasingly common, but its safety in patients with hyperthyroidism has not been well studied.

METHODS

This retrospective study reviewed 183 patients with hyperthyroidism who underwent total thyroidectomy from 2015 to 2022 at one urban, academic center. The main outcomes were rates of thyroid storm, surgical complications, and 30-day ED visits and readmissions.

RESULTS

Among 183 patients with hyperthyroidism (mean age, 45 ± 14.5 years; 82.5% female), there were no cases of thyroid storm and complications included recurrent laryngeal nerve (RLN) palsy (7.0%), symptomatic hypocalcemia (4.4%), and hematoma (1.6%). ED visits were present in 1.1% and no patients were readmitted.

CONCLUSION

Total thyroidectomy was not associated with thyroid storm and <6% of patients required inpatient management. Ambulatory total thyroidectomy for hyperthyroidism warrants further consideration through identification of predictive factors for postoperative complications.

Imaging features of intra-abdominal and intra-pelvic causes of hirsutism

Hirsutism is a relatively common disorder which affects approximately 5% to 15% of women. It is defined by excessive growth of terminal hair in women, which primarily affects areas dependent on androgens, such as the face, abdomen, buttocks, and thighs. Hirsutism can be caused by a variety of etiologies, which are most often not lifethreatening. However, in some cases, hirsutism can be an indicator of more serious underlying pathology, such as a neoplasm, which may require further elucidation with imaging. Within the abdomen and pelvis, adrenal and ovarian pathologies are the primary consideration. The goal of this manuscript is to review the etiologies and imaging features of various intra-abdominal and intra-pelvic causes of hirsutism.

PSAT192 Hypercalcemia of Immobility in a Patient with Post-Surgical Hypoparathyroidism

Background

Hypercalcemia of immobility is a rare diagnosis in the general population, and thus requires careful evaluation to rule out other causes of non-PTH mediated calcium excess. The pathogenesis is not clearly established, however, likely involves a reduction in mechanical loading stimulus from osteocytes with resultant decreased bone formation and increased bone resorption. Management requires careful assessment to maintain normal calcium. We present a case of hypercalcemia of immobility in a patient with a known history of surgical hypoparathyroidism.

Clinical Case

A 64-year-old man with a history of transglottic cancer s/p total laryngectomy and tracheostomy with resulting post-surgical hypoparathyroidism and hypothyroidism presented for a tracheostomy change and was found to be hypercalcemic. Since his laryngectomy four years ago, the patient had a low PTH of 2.9 pg/mL (10.0 - 65.0 pg/mL) with resulting prolonged hypocalcemia from 5.9 to 7.9 mg/dL (8.5-10.5 mg/mL) requiring calcium and daily calcitriol treatment. Four months prior to current hospitalization, he developed avascular necrosis of the hip and became essentially bedbound from severe hip pain. Since immobilization, his calcium was noted to increase, with the highest corrected calcium of 10.9 mg/dL (8.5-10.5 mg/mL), necessitating tapering and eventual discontinuation of calcium supplements and calcitriol. During this admission, corrected calcium was 12 mg/dL (8.5-10.5 mg/mL). PTH-rP was 16 pg/mL (14 - 27 pg/mL), PTH was 11.2 pg/mL (15-65 pg/mL), vitamin D 25-hydroxy total was 14.7 ng/mL (30-60 ng/mL), 1,25 dihydroxy vitamin D was 18.2 pg/mL (19.9 to 79.3 pg/mL), SPEP did not detect monoclonal protein, thyroid function was normal and bone scan showed no evidence of metastasis, thus excluding other causes of hypercalcemia. Bone specific alkaline phosphatase was 11.7 (7.6-14.9 mcg/L). C-telopeptide, a marker of bone resorption, was markedly elevated at 2079 (87-345 pg/mL), suggesting hypercalcemia of immobility. The patient was started on vitamin D supplementation, intravenous fluid hydration and physical therapy was initiated to encourage mobilization. The patient was carefully monitored with regular labs to avoid the risk of hypocalcemia once mobilization improved. His calcium began to decline to 10.5 (8.5-10.5 mg/mL) at time of discharge, eventually requiring calcium and calcitriol supplementation to maintain normocalcemia.

Conclusion

Hypercalcemia of immobility should be suspected in patients witha history of post-surgical hypoparathyroidism who present with new onset hypercalcemia that persists despite titrating or discontinuing calcium and calcitriol therapy. It is a diagnosis of exclusion and thorough laboratory assessment is needed to rule out other causes of hypercalcemia. These patients are at risk of hypocalcemia once the underlying etiology is corrected i.e restoration of mobility. Therefore, bisphosphonates should be avoided for acute treatment of hypercalcemia unless refractory to intravenous hydration. Once mobilization improves, calcium levels should be carefully monitored, and calcitriol and calcium supplementation should be resumed to maintain normocalcemia.

Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.

PSUN61 Primary Aldosteronism Presenting as Chronic Hypokalemia in a Normotensive Patient

Introduction

Conn first described the hallmark features of primary aldosteronism (PA) as a state of aldosterone excess in the setting of hypertension and hypokalemia. Recent work has shed light on a wide spectrum of disease that likely includes normotensive patients with elevated aldosterone and suppressed renin. Mineralocorticoid excess appears to be the main driver of disease progression; however, it is not known whether individual differences in intra-arterial plasticity and effective sodium potassium exchange alter the overt clinical presentation. Here, we describe a patient with chronic hypokalemia and normal blood pressure with the diagnosis of a unilateral aldosterone-producing adenoma.

Clinical Case

A 47-year-old woman with no significant medical history was referred to endocrinology for evaluation of isolated hypokalemia since 2012. Her potassium was 2.8mEq/L at its lowest a month prior to her visit and had numerous other values less than 3.5mEq/L over the past 10 years. She did not carry a diagnosis of hypertension nor was she hypertensive at the time of her initial and subsequent evaluations. Results on initial endocrinology evaluation demonstrated a potassium of 3.2mEq/L (3.5-5.0mEq/L), Plasma Aldosterone Concentration (PAC) of 29ng/dL (≤21ng/dL), Plasma Renin Activity (PRA) of 0.42ng/mL/h (0.25-5.82ng/mL/h), and Aldosterone Renin Ratio (ARR) of 69. PA was suspected based on hypokalemia with an ARR >30 and PAC >20ng/dL. Further work-up was pursued to confirm the diagnosis as the patient did not have hypertension. She underwent 3-day oral sodium loading. 24-hour urine collection at the conclusion revealed adequate sodium loading with a urine sodium content of 208mEq/24hr (>200mEq/24hr) and aldosterone secretion of 41.3mcg/24hr (<12mcg/24hr). She subsequently underwent a CT abdomen demonstrating a 1.3×0.8 cm right adrenal nodule. Adrenal venous sampling was performed (continuous cosyntropin infusion with simultaneous adrenal venous sampling) which revealed a cortisol-corrected aldosterone lateralization ratio (right to left) of 406 at -5 minutes, 368 at 0 minutes, 33 at 10 minutes and 85 at 15 minutes. Results were consistent with strong lateralization to the right with contralateral suppression. Diagnosis of a right-sided aldosterone-producing adenoma was confirmed and she was referred to surgery for right adrenalectomy.

Conclusion

This case highlights one of the many presentations of PA. The persistent hypokalemia for a decade suggests a history of longstanding untreated PA prior to eventual diagnosis, yet the patient has remained normotensive. Though normotensive PA is a recognized entity, most patients develop hypertension within 5 years. The ability to remain normotensive despite intravascular volume expansion may highlight the patient's highly compliant vasculature and kidneys that have likely adapted to excrete high sodium loads in the setting of sodium excess. This case emphasizes that isolated hypokalemia in patients without hypertension should prompt consideration of PA and that patients with PA may maintain normotension for multiple years.

Presentation: Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m.

Synchronous Malignant Pheochromocytoma With Renal Cell Carcinoma: A Case Report

Introduction: In the US, Pheochromocytoma/paraganglioma incidence is estimated to be 2–8 per 1 million people each year with around 100–200 of these cases being malignant. Malignant pheochromocytoma is defined by documented presence of metastases or evidence of extensive local invasion. There are certain genetic syndromes which are also associated with renal cell carcinoma, including SDHB mutations type 4, VHL disease and familial pheochromocytoma. These syndromes are important to recognize as they may signify a worse prognosis. Here, we describe a case of co-occurrence of malignant PC with renal cell carcinoma.

Case Report: A 53-year-old Hispanic male with history of HTN and recently diagnosed metastatic pheochromocytoma was admitted for surgical debulking of the left retroperitoneal/adrenal and renal masses. Symptoms began five months prior after he presented with an ischemic stroke in the setting of labile hypertension. He was diagnosed with a 6.3 x 4.6 x 6.8 cm incidental left retroperitoneal mass and suspicious left renal mass on CT imaging but also noted several lytic bony lesions concerning for bone metastasis. A spinal biopsy was obtained which was consistent with a well-differentiated metastatic neuroendocrine tumor. Laboratory evaluation was notable for Chromogranin A level of 6959ng/mL (25–140). He was started on Lanreotide. Given persistently difficult to control HTN he underwent work up for secondary hypertension. Hormonal evaluation was notable for plasma free metanephrine of 534pg/mL (<57pg/mL), normetanephrine 6155pg/mL(<148pg/mL), and total metanephrine of 6689pg/mL (205pg/mL) consistent with metastatic Pheochromocytoma. After appropriate alpha blockade he underwent left adrenalectomy, nephrectomy and liver tumor microwave ablation. Pathology was consistent with an 8.7cm pheochromocytoma with extensive retroperitoneal soft tissue invasion and PASS score of 9 as well as a 3.6 cm renal cell (clear cell-papillary type) carcinoma. On follow up, Plasma metanephrine decreased significantly postoperatively to a free metanephrine of 28pg/ml, normetanephrine 1153pg/ml, and total metanephrine of 1181pg/mL. He was referred for genetic testing but unfortunately, he was readmitted one month later with cerebral hemorrhage and expired.

Conclusion: Advancements in genetics have led to improved understanding of the molecular etiologies of pheochromocytomas. A number of genetic defects are associated with PC and RCC, including SDHB mutations type 4, VHL and familial pheochromocytoma. Our case underscores the high morbidity and mortality in patients with metastatic PC with RCC and perhaps the catastrophic outcomes in such patients. Assessing patient’s genetics in these cases is now the standard of care, however further research studies are warranted to better understand the significance of tumor genetics on prognosis and management.

Testosterone Use and Adrenal Hemorrhage

Background: Testosterone supplementation has been associated with a variety of side effects, such as polycythemia, and can potentially increase the risk of cardiovascular disease. Testosterone use has also been associated with increased thrombotic events, especially in patients with underlying hypercoagulable state. Clinical Case: A 57-year-old man presented with abdominal pain and distention. He had history of previous intramuscular (IM) and oral testosterone use for ten years. For 8 weeks prior to initial presentation, he reported using weekly IM 500mg Testosterone injections. Computed Tomography (CT) of the abdomen and pelvis revealed multiple thrombi of the portal, splenic, superior mesenteric and inferior mesenteric veins. He was started on Warfarin and discharged home. A few weeks later, he presented with similar symptoms with labs now showing an International Normalized Ratio (INR) of 10.2. Repeat CT was significant for presence of bilateral adrenal hemorrhage, measuring 2.9cm on the right and 2.4cm on the left, which were not seen on previous imaging done one week prior. During the hospital course, he was found to be hypotensive with low platelet count so Intravenous Immunoglobulin therapy was initiated for suspected catastrophic antiphospholipid syndrome (CAPS). Morning cortisol was 5.82 ug/dL (6.2–29.0) so this critically-ill patient was started on stress dose hydrocortisone, which was subsequently tapered to physiological dose after clinical improvement. Cosyntropin stimulation test was performed after withholding the prior dose of hydrocortisone. The baseline cortisol was 0.88 ug/dL (6.20–29.00ug/dL), after administration of 250mcg of Cosyntropin 30- and 60-minute cortisol levels were 1.5 ug/dL (4.3–22.4ug/dL) and 1.6 ug/dL (4.3–22.4ug/dL) respectively. Baseline ACTH of 121.0 pg/mL (7.2–63.3pg/mL), consistent with primary adrenal insufficiency. Dehydroepiandrosterone Sulfate (DHEA-S) level was 15.7 ug/dL (80.0–560.0ug/dL). Hypercoagulability workup was significant for the presence of lupus anticoagulant and antibodies positive for heparin induced thrombocytopenia, so patient was diagnosed with Antiphospholipid syndrome. Conclusion: This is a case of hypercoagulability in a patient with history of anabolic steroid misuse who developed extensive intraabdominal venous thrombosis, adrenal hemorrhage, and primary adrenal insufficiency. Adrenal vein thrombosis and hemorrhage can be life threatening sequalae of testosterone misuse and should be considered in the differential for patients with history of testosterone misuse and adrenal insufficiency.

Evaluation of Adrenal Vein Sampling Use and Outcomes in Patients With Primary Aldosteronism

BACKGROUND

Primary aldosteronism (PA) occurs in 10%-20% of patients with resistant hypertension. Guidelines recommend adrenal vein sampling (AVS) to identify patients for surgical management. We evaluate the use of AVS in managing PA to better understand the selection and outcomes of medical versus surgical treatment.

METHODS

A retrospective review was performed, and patients were divided into those who did (AVS) and did not have AVS (non-AVS). Demographics, aldosterone and renin levels, blood pressure, comorbidities, and antihypertensive medications were recorded. Reasons to defer AVS and medical versus surgical decision-making were examined and groups were compared.

RESULTS

We included 113 patients; 39.8% (45/113) had AVS, whereas 60.2% (68/113) did not. Groups were similar in age, body mass index, and initial systolic blood pressure (SBP). In patients who underwent AVS, 31 of 45 (68.9%) had unilateral secretion and were referred for surgery, whereas 13 of 45 (28.9%) had bilateral secretion. Of the 31 referred for surgery, 26 underwent laparoscopic adrenalectomy, all cured; four refused surgery; and one counseled toward medical management by their physician. In 68 non-AVS patients, 6 (8.8%) underwent adrenalectomy without sampling and 2 with no clinical improvement. The remaining deferrals were because of normal or bilateral adrenal nodules on imaging (8/68, 11.8%); medical management due to poor surgical candidacy (12/68, 17.6%); patient refusal of intervention (13/68, 19.1%); or reasons not stated (28/68, 41.1%). At the follow-up, patients who underwent AVS had lower median SBP (135.4 mmHg versus 144.7 mmHg, P = 0.0241) and shorter follow-up (17.7 mo versus 54.0 mo, P < 0.0001). Surgically managed patients had biochemical resolution of PA with normalization of potassium levels (3.6 to 4.7mEq/L, P < 0.00001).

CONCLUSIONS

AVS correctly selects patients for surgical management avoiding unnecessary surgery. However, despite guidelines, AVS is not always pursued as part of PA treatment, potentially excluding surgical candidates.

SAT-242 Isolated Adrenocorticotropic Hormone Deficiency Secondary to the PD-1 Inhibitor Pembrolizumab

Background: Immune checkpoint inhibitors (ICI’s) are now indicated in the treatment of several solid tumors and have improved the prognosis of patients with advanced malignancy. The expanded use of ICI’s has led to the rise of otherwise rare autoimmune sequelae. The overall incidence of ICI-induced autoimmune hypophysitis has increased to approximately 10%, but is only estimated to be 0.4% with PD-1 inhibitors specifically (1). Isolated ACTH deficiency from immune checkpoint inhibitors is rare, and very few cases secondary to the PD-1 inhibitor pembrolizumab have thus far been reported.

Clinical Case: A 75-year old woman with history of Stage IV lung adenocarcinoma presented to oncology clinic in July 2019 with progressive weakness, weight loss, and confusion for several weeks. She was found to be hypotensive and dehydrated in the clinic and subsequently was admitted to the hospital. A comprehensive infectious work-up was non-contributory. History revealed that after treatment failure with carboplatin, she was treated with pembrolizumab from January 2017 to June 2019 with excellent response. Laboratory evaluation on admission demonstrated an undetectable AM cortisol level of < 1 ug/dL (n 5-25 ug/dL) with concomitant ACTH < 5pg/mL (Roche cobas, n 7.2-63 pg/mL), consistent with central adrenal insufficiency. Testing of the remainder of the pituitary axis, including TSH (0.83uU/mL, n 0.4-4.6 uU/mL), FSH (34.7 mIU/mL, n <150mIU/mL), LH (12.6mIU/mL, n <60 mIU/mL), and IGF-1 (33ng/mL, n 34-245ng/mL), all returned within normal limits. Further chart review verified that she had not been exposed to any form of glucocorticoids within the past 6 months. MRI brain with contrast demonstrated no obvious pituitary disease. The patient was started on 5mg of prednisone daily, with significant improvement in mental status, appetite, and blood pressure. She was discharged home on maintenance prednisone for adrenal insufficiency due to presumed isolated corticotroph destruction.

Conclusions: Isolated ACTH deficiency is a very rare but potential consequence of pembrolizumab use. It can be especially difficult to diagnose in patients on chemotherapy who are at higher risk for dehydration and failure to thrive. Duration of pembrolizumab therapy should not preclude the diagnosis of isolated ACTH deficiency, as it can occur even as late as 2.5 years into therapy.

Reference: (1) Chang, L., Barroso-Sousa, R., Tolaney S., Hodi F.S., Kaiser, U.B., Min, L. Endocrine Toxicity of Cancer Immunotherapy Targeting Immune Checkpoints, Endocr Rev. 2019;40;17–65.

MON-452 Poorly Differentiated Thyroid Carcinoma Metastatic to the Adrenal Gland

Background: Poorly differentiated thyroid carcinoma (PDTC) constitutes 1-15% of all thyroid cancers.¹ Invasive adrenal metastases secondary to PTDC are exceedingly rare.

Clinical Case: A 64-year-old woman with a non-toxic multinodular goiter presented with right upper quadrant abdominal pain and distension for three months. CT imaging revealed a 13.5 cm right suprarenal retroperitoneal mass invading the liver and inferior vena cava (IVC), concerning for adrenocortical carcinoma. She underwent resection of the mass with en block right adrenalectomy, partial hepatectomy, and IVC resection. Pathology demonstrated metastatic thyroid cancer with necrosis of the adrenal gland and IVC. Immunohistochemical staining was positive for PAX8, TTF1, and thyroglobulin (Tg). Completion thyroidectomy revealed an encapsulated 2 cm focus of PDTC with Hurthle cell phenotype in the right thyroid lobe. The mitotic activity was 5/10 per HPF. There were focal areas of tumor necrosis, 3 foci of capsular invasion, and extensive angioinvasion. Surgical margins were free of tumor invasion. Eight resected lymph nodes were negative for malignancy (Stage T1bN0M1; AJCC 8, Stage IVb). Genetic testing was positive for somatic mutations of NRAS, TERT, PTEN, and GNAS with broad copy number loss on chromosome 22q conferring aggressive tumor behavior.³

MRI of the brain and spine ruled out additional metastases. A radioactive iodine (RAI) whole-body scan (WBS) showed residual uptake of 7.6% in the right thyroid bed and a focus of increased uptake at the right sternoclavicular joint. A therapeutic dose of 206 mCi of I-131 was administered. A post-therapy WBS demonstrated focal activity in the right thyroid bed, distal right clavicle, and lower lung lobes. Chest CT and MRI of the right shoulder revealed no structural evidence of metastases corresponding to radiotracer uptake. The stimulated Tg level prior to RAI was 323 ng/mL with a TSH of 66 uU/mL (0.4-4.6 uU/mL). Tg antibodies were undetectable. She was maintained on 150 mcg of levothyroxine with the goal of TSH suppression. Tg levels declined to 4.8 ng/mL at three months, and to 0.3 ng/mL eight months post-RAI.

Discussion: PDTC is an aggressive thyroid cancer subtype with distant metastasis reported in 36-85% of cases.² Distant metastasis is predictive of poorer outcomes, with patients three times more likely to die from the disease than those without metastatic disease.¹ Adrenal metastasis of thyroid cancer is rare, and unlike in our patient, usually asymptomatic and frequently detected on a post-therapy scan. Despite a dramatic response to therapy, given the poorly differentiated features of the primary tumor, a whole-body PET-CT is warranted to evaluate for RAI refractory disease.

References:

1. Ibrahimpasic T et al. J Clin Endocrinol Metab. 2014;99(4):1245-52.

2. Sanders EM Jr et al. World J Surg. 2007;31(5):934-45.

3. Cheng DT et al. J Mol Diagn. 2015;17(3):251-64.

SAT-323 Thoracic Paraganglioma Presenting with Recurrent Cerebrovascular Events

Background: Thoracic spine paraganglioma precipitating acute stroke is extremely rare. We report a case of a patient with thoracic paraganglioma at high risk for spinal cord compression with recurrent cerebrovascular events. Clinical Case: A 59 year old male was admitted for transient right hemiplegia after recent admission for right lacunar CVA. The patient was noted to have episodes of labile hypertension, sinus tachycardia and paroxysmal diaphoresis. Five days after admission, he developed ataxia with right pronator drift and was treated with intravenous thrombolytics for suspected acute CVA. Incidentally, an 8 cm thoracic paraspinal necrotic mass invading T10 and T11 vertebral bodies with impending cord compression was found on imaging. CT-guided needle biopsy of the mass was performed. Pathology showed an oval and spindle cell neoplasm staining positive for synaptophysin and chromogranin, favoring paraganglioma. Chromogranin A was elevated 472 ng/mL (25 - 140 ng/mL). Plasma free metanephrines were 32 g/mL (n < 57 pg/mL) and plasma free normetanephrines were 7690 pg/mL (n < 148 pg/mL). MIBG scan showed focus of increased uptake at T10 and T11 as well as in the left posterior eighth rib and peri-aortic region. Subsequently, the patient developed acute right leg weakness and dysmetria; MRI brain confirmed acute infarct in the posterior limb of the left internal capsule. Alpha blockade followed by beta blockade was initiated. After approximately 2.5 weeks of alpha blockade, the patient underwent spinal angiogram with tumor embolization followed by successful en bloc tumor resection by neurosurgery and cardiothoracic surgery. Final pathology showed a 7.5 cm paraganglioma which demonstrated some aggressive pathologic features including Ki67 index>20% and 10% focal necrosis. Post-operative plasma free normetanephrines decreased to 568 pg/mL and metanephrines were undetectable. Genetic testing utilizing Ambry Genetics PGLnext panel was negative. Conclusion: A differential diagnosis of paraganglioma should be considered in any patient presenting with recurrent stroke and paraspinal mass. Biopsy should be avoided. Timing of surgical resection to decrease risk of further cerebrovascular compromise is challenging and requires a multidisciplinary approach (1). Locally invasive paragangliomas are rare and are often associated with SDHB mutations; however, a full genetic analysis did not identify any known genetic mutations. Reference: (1) Oak, S., Javid, M., Callender, G., Carling, T., Gibson, C. Management of pheochromocytoma in the setting of acute stroke. AACE Clinical Case Reports 2018 4:3, e245-e248.

Metformin regulates metabolic and nonmetabolic pathways in skeletal muscle and subcutaneous adipose tissues of older adults

Administration of metformin increases healthspan and lifespan in model systems, and evidence from clinical trials and observational studies suggests that metformin delays a variety of age‐related morbidities. Although metformin has been shown to modulate multiple biological pathways at the cellular level, these pleiotropic effects of metformin on the biology of human aging have not been studied. We studied ~70‐year‐old participants (n = 14) in a randomized, double‐blind, placebo‐controlled, crossover trial in which they were treated with 6 weeks each of metformin and placebo. Following each treatment period, skeletal muscle and subcutaneous adipose tissue biopsies were obtained, and a mixed‐meal challenge test was performed. As expected, metformin therapy lowered 2‐hour glucose, insulin AUC, and insulin secretion compared to placebo. Using FDR<0.05, 647 genes were differentially expressed in muscle and 146 genes were differentially expressed in adipose tissue. Both metabolic and nonmetabolic pathways were significantly influenced, including pyruvate metabolism and DNA repair in muscle and PPAR and SREBP signaling, mitochondrial fatty acid oxidation, and collagen trimerization in adipose. While each tissue had a signature reflecting its own function, we identified a cascade of predictive upstream transcriptional regulators, including mTORC1, MYC, TNF, TGFß1, and miRNA‐29b that may explain tissue‐specific transcriptomic changes in response to metformin treatment. This study provides the first evidence that, in older adults, metformin has metabolic and nonmetabolic effects linked to aging. These data can inform the development of biomarkers for the effects of metformin, and potentially other drugs, on key aging pathways.