Unfortunately, lung cancer is common among heavy smokers. Thus any concerning symptoms in someone that has smoked for a long time warrants and immediate evaluation for lung cancer. The best type of physician to see initially is a primary care physician
such as a family doctor
or internal medicine doctor. If lung cancer is found, then he would need a referral to an oncologist
that specializes in lung cancers.
Symptoms of lung cancer include cough, shortness of breath, weight loss, generally feeling tired. Your husband's symptoms of weight loss over 6 months (that I assume was not intentional) along with low appetite in the context of a heavy smoking history is VERY concerning for lung cancer. I am especially concerned because he has not seen a doctor in some time, so his cancer may being going undetected. His pallor may be due to anemia (or low red blood cells), a common finding in anyone with cancer.
I suggest that you make an appointment for your husband to see his primary care physician today. He will need a more detailed evaluation of his symptoms along with a thorough physical exam. Likely, he will need some chest imaging which may start with a chest x-ray then a CT scan. Good luck.