Being a Marine taught me the importance of giving back. But my last mission may be my most crucial: instilling the same values in my son.

Two years ago, I was built like a tank. I’ve been built like that my entire life, having grown up as a wrestler in high school and college. Once, way back then, someone looked at me and said, “What the hell are you?”

I look much different now. It’s hard for me to speak for long periods of time, and I’m about half the size I used to be. Now, I’m happy to just get up and walk, which is a mental challenge all by itself. The guy I used to be has been destroyed by chemotherapy.

In late 2015, I was diagnosed with stage-four cholangiocarcinoma, a rare and aggressive form of cancer that starts in the bile ducts. I don’t know how much time I have left; I may not even make it to my 55th birthday this December. But I’m happy that I can go knowing I’ve lived my life in complete service to others and to my family.

Except I have a teenage son, and there’s still so much to teach him.

I won’t be able to impart my wisdom to Mason as he grows up. That’s why I’m making sure he knows now the importance of living a life in service, like I have. The lessons are simple: Be humble, be open and be helpful.

Growing up, my father was constantly working, which meant he wasn’t around a ton. He did the best he could though, and I considered him my best friend. But I didn’t have someone who could mentally challenge me. I got into wrestling in the seventh grade, and my coach became that person for me instead. He ended up being a formidable figure in my life, and I’m still in touch with him today.

You could tell immediately that this man had served in the military — through his mannerisms, his attention to detail and his level of concentration. I thought, “This guy is incredible.” At an early age, my coach gave me advice that to this day I continue to take to heart:

“Don’t be a wise guy,” he would tell me. “Don’t be a showboat.”

Eventually, I joined the Marines, and that advice is what got me through basic training. Now, it’s something I teach Mason at every opportunity. We have a lot of big talks these days — especially now that I don’t know how long I have left to live — and I try to tell him who I was before the military.

I tell him not to be that guy.

When I enlisted in 1982, I was a very private person. In fact, you could say I was pretty closed off. But interaction with people is important, and you have to be open and outgoing. There is just something about being open to new experiences that makes life more meaningful. It also makes you not afraid to help people.

There is nothing more gratifying than helping others, and there are many avenues for doing that — not just through the military.

I joined the Marines after one year of college because I simply didn’t know what I wanted to do with my life. In fact, the movie “An Officer and a Gentleman,” about a guy who joins the Navy, came out right before I signed up, and that shaped what I thought the military was going to be like.

I was wrong.

My time in the military wasn’t like a Richard Gere action-romance film. It was tough, and it was terrifying. But it also made me grow into a man that started to think to myself, “What can I do to give back?” What the Marines did was laser-focus my attention and instilled in me the idea that, “Hey, you’re capable of a hell of a lot more than what you’re doing now.”

I left the service in 1988, and it haunted me for a long time. I just missed it so badly. I still say that the Marine Corps was the best job I ever had. But I can no longer regret leaving, because I have the best family God could give me, and I would never have met my wife and had Mason if I had stayed.

But here’s the thing: When you serve, the experience never truly leaves you; it always stays with you. Every time something tragic occurred, I would quietly shed a tear. When 9/11 happened, I was choked up watching the coverage on TV. I felt like I should be there — I needed to help.

So off I went to Ground Zero, wearing my old and dated fatigues from the ’80s, and was able to get my way onto the search and rescue team that pulled out the first five people. It was surreal; everyone had the same look on their face, much like how they talk about the empty thousand-yard stare of soldiers who served in Vietnam. There was a gray, pinkish powder in the air, like debris mixed with blood. And it covered everything.

My cancer, my family and I believe, has a direct correlation to my time helping on the pile. But I wouldn’t take any of it back, and Mason knows that.

And that’s because service is part of me, now. I tell Mason constantly that being in service is such a selfless act. It’s contributing to something bigger than yourself. It just requires humility and the willingness to be open to help others.

Luckily for me, Mason already has most of these traits. But he’s only 14 and has a lot of growing up ahead of him and will face situations where I won’t be there to talk to him.

And that is the one thing that kills me — figuratively, of course — feeling like I’ve let down my son by dying too soon.

He’s talking right now of going to the Naval Academy in Annapolis, Md. I hope he does. He’s smart and creative, and good in science and math. I can see him being a biomechanical engineer or something similar.

But even if he doesn’t go into military, I just want him to be happy helping people. I tell him that if he sees someone who needs help, help them. It’s a really good feeling. I promise.

As told to NationSwell staff writer Joseph Darius Jaafari. This essay has been edited for clarity an style. Read more stories of service here.

Update: Anthony Egan passed away on Sunday, Nov. 19, 2017, with his family by his side. He served as a corporal in the intelligence unit of the U.S. Marines from 1982 until 1988. He then spent more than 20 years working in the pharmaceutical industry. He is survived by his wife and son in New Jersey.