Hi and welcome to HCM.
If you think of cancer metastasis
it is always possible,but isnt usual in this place. IT can be basal pulmonary infection(esepcially considering your low WBC) or stomach and spleen issue. Also chemo and radioth have effect on many organs including spleen and liver.I suggest to do abdominal ultrasound
and chest xray and everything will be clear. If you have reathing difficultis,vomiting
or sharp pain
around heart and left shoulder you should go to hospital as soon as you can.
Wish you good health.