hi,

thank you for providing the brief history of you.

since you mentioned you had cancer in the past and I am sure it is treated well. Now as you are facing pain in the collar bone while breathing in and out right above the breast level.

so understand this and make more precise the pain region is in between the collar bone and 4th intercostal space.

On a safe note it is better to get the heart checked once by a cardiologist and also to take an x-ray of that area so the superior lobe of the lung will be exposed and will be assessed further. This is just to rule out if you have any systemic pathology.

Also coming to the pain, if it is muscular you can do some gradual massage in that area as the spasm of the respiratory muscles can be reduced by the same. Doing regular deep breathing exercises and costal breathing exercises will help improve the capacity of the lungs and also strengthen the muscles of the chest.

You can slowly progress to the upper limb exercises which will help to add on some more strength of the pectoralis muscle.

Perform some slow static neck exercises as it will also help strengthen the secondary muscles of respiration like the sternocleidomastoid and scalenous group.

Since you had a pathology of squamous cell in the past the weakness of the accessory muscles of respiration is a chance. Doing breathing exercise will help improve the strength and reduce the pain.

also to add on, that breathing exercises will even help the cellular physiological to the optimal as the cellular mechanism needs improvement too avoid any further occurance of the squamous cell.

with the grace of God I wish you a good health.

Regards.
Jay Indravadan Patel