How would you manage a patient with anal squamous cell carcinoma and 5 FU induced coronary vasospasm 36 hours after starting definitive chemoradiation?

I would seek the assistance of an oncocardiologist, if available. Did the patient develop EKG changes? Troponin leak?

For coronary vasospasm induced by 5FU, there is a range of severity and risk. Given that this patient only requires a second dose of 5FU, I would see if there were any possibility of giving the drug safely including with titration of vasodilators (CCB and/or oral nitrates) prior to C2 until intolerable by BP. While we have patients with ST elevation and troponin leak whom we are unwilling to re-expose, we also have patients that we admit for 5FU infusion for close monitoring and management. This may be on the floor or ICU depending on assessed risk. Interventions include use of continuous infusion of intravenous nitrates, an...

I'm not sure if this is helpful to you in this situation, but in a different GI cancer, I was pleased to learn recently that it is the infusional 5 FU that causes vasospasm that is also seen with capecitabine; bolus 5 FU may be safe to use. See the reference below:

Safety and tolerability of the bolus 5 fluorouracil based FLOX and IFL regimens in pts who developed fluoropyrimidine-induced coronary vasospasm during therapy with infusional 5-FU or capecitabine

Journal of Clinical Oncology 2018 36:15_suppl, e15513

If the cancer is early staged or non bulky, consider forgoing further 5FU and finish with mitomycin as planned and slightly higher radiation boost dose. If the cancer is bulky/advanced stage, I would change the regimen to perhaps carbo/tax. Both options would allow a safe alternative.