Thank you to all you wonderful people who have responded with caring and thoughtful answers. Now, has anyone experienced this cancer?

You can look up all these genetic markers for the cancer, Pha, but the basic problem is the last words which are that this is stage IV and that it is metastasized. Stage IV cancer means basically that it is not "curable" and that you are likely to die of cancer as your diagnosis unless you walk in front of a car or truck before that. Metastasized means spread. You do not apparently know where it has spread to. Breast cancer usually spreads to the brain or the bones or the lungs, but that doesn't rule out other areas. Can go to the liver. Tests called PET scans will basically tell them what portions of the body "light up" and that is where they will test for spread. After that it is up to an oncology and a radiation team to do whack-a-mole, treating the problems that exist and treating new problems when they come up.
You should use your computer to look up things. 1) Metastasized cancer 2)Stage IV cancer of the breast. Anything else you want. The Her2 and estrogen + or - less important to look up. They have genetic consequences for your daughter's children more than anything else.
This is going now to be a family in shock and afraid. That said, things will go a day at a time, and your job is NOT to tell your daughter she will be fine (she may not be, so that would be a lie). Or that "prayer" or burning sage or coffee enemas might cure her (they will not though dependent on her feelings they may be a comfort). And NOT to tell her that she can cure herself. That puts an added burden on someone who got this illness for no reason and who, the hope is, MDs will keep alive for many many more years.
Your daughter will be given treatment options. They will include or MIGHT include mastectomy or lumpectomy with radiation, chemotherapy, radiation therapy. All are weakening and tough to get through. Your help with cooking, driving, helping with the kids will be a huge help.
Allow your daughter to give HER OWN feelings. If she wants to plan a funeral with photos and music, let her, telling her you hope it is 70 years in the future. If she wants to deny that stage IV could take her life, let her. That is, let her be or say or do WHATEVER SHE WANTS. Tell her you are sorry when she is sad, tell her you love her, tell her to let you know what you can do to help. Her moods will be swinging every which way for a while.
I had stage II cancer (spread to two lymph nodes) 35 years ago. Fought it with mastectomy and chemo. Am still alive at 80 with no recurrance. Stage IV is tougher but there are new treatments ALL THE TIME every day, very targeted and can keep people alive for many many many years.
Just basically be there for her. Let he handle this with her own family and offer help. I am so dreadfully sorry. As a nurse I know this is tough. And as a survivor.
Take this one day at a time and make GOOGLE your best friend. Look up everything. Don't share info with her unless she wants it. I was overwhelmed with too much information at first.
Basically, be a listening post. Cook. Clean. Watch the kids. Be certain she plans GOOD and happy things to do along with all the awful things she will have on her place. Even if they are plans for times ahead like Paris in 2030.
This will be a hard year for you all. Tell her you want to share what she wants to share and are strong enough to hear it. Let her be honest with you. Tell her you are fine if she does NOT want to share anything.
She's the boss basically. I am glad she has such a good man at her side and I am so very sorry for your loss of your wife.

Don't burden yourself by getting into the weeds about the particulars of the diagnosis. As Alva said, metastatic means it has spread, and Stage IV is the bad version. (It's been in her body for a while.)

Focus on the family stuff. Be a sympathetic ear for both your daughter and her husband, as he's going to need support, too. He's now a caregiver as you were, and he needs a safe place to fall apart if he needs to.

Work on making memories for those kids. If you have a cell phone, take pictures of their mama, put together photo albums of her when she was growing up, and write down memories you have of her growing up. Those kids will want to know about her, and they'll want to know about you, too, so write down memories of your own childhood, too. It doesn't have to be great writing -- anecdotes are fine -- but preserve that history for them.

Keep close to those kids. Help their folks as much as you can as they ask. Do what you can do, but also don't neglect yourself and your grief. Keep going to those groups.

Dear ed
i don’t have much advice I’m afraid but I think your daughter knowing her dad is such a wonderful man and is there to support her, her husband and kids will lift her. I would start with a website specialising in breast cancer - over here in the uk we have an organisation called macmillan nurses who would give lots of advice maybe you have something similar in the us
I send your daughter all the best of luck and to you a huge hug
Much love to you Ed and to your family xxx

I'm so sorry to learn of your daughter's cancer diagnosis. 
Alva has offered good insights, especially as to the contributing factors.   I would unfortunately have to agree that Stage IV is an advanced stage.   

Remembering what my father, my sister's friends and I did for her after her D/x also of advanced cancer, perhaps these suggestions would help:

1.   If she elects to get chemo, it could just wear her down.   And she may lose her appetite, or find it so severely limited that it's hard to find food she can or wants to eat.

2.  If eating becomes an issue, we found that juices (w/o all the additives) helped; at one point that was all that she could tolerate.   Tastes can vary during chemo.

3.  I hate to relate this, but it's helpful to know.  If the cancer metastasizes to her brain, other aspects of her body could be affected.

     a.  Brain:  some confusion may result.  Be prepared for you or her husband to take over financial management, etc. before the cancer reaches that stage.   Take responsibility for as much as the family can to redirect attention on household and financial issues so she doesn't have to be concerned about them.

     b.   Spinal cord:   this metastasis caused "drop foot", a condition in which control is lost over a foot, and it can turn outward.    My sister was fitted with a type of brace, but it was uncomfortable, awkward to use, and that situation was very, very emotional, especially since she had been a runner.

     c.    Spinal cord:   she had trouble standing, had to crawl to the door to let the dogs out.  That's when I moved in with her.    I had someone help bring down a mattress and slept on it next to the large couch which she then used for a bed.  It was easier to get in and out of than a bed.   Eliminate as much as you can that requires movement up or down stairs, or in areas where there are no handholds or grab bars.  If you do install them, use only a licensed carpenter.  

      d.    Spinal cord:   You can consider what needs to be done in the house in terms of moving around, create a bedroom on the first floor, close to a bathroom, and avoid climbing stairs.  Get some no rinse shampoo and soap so she can still feel clean, but avoid hazards like showers and bathtub (especially a bathtub!)

      e.    Warmth:   the body can't always maintain heat, so have plenty of warm blankets and heavy sweaters available.   Nightgowns are easier to get in and out of than pajamas, and better for midnight overnight bathroom visits.  Get heavy or hunting socks for her feet.

4.    If she has chemo, be aware of a condition that in 2003 was known as "bacterial showers".   It occurs after chemo infusion, when the chemo nurse uses (sterile?) water to clean the port (a device that's inserted in the chest area or thereabouts to hold the chemo line as it runs into the body.   It's cleaned afterward.  

My sister, who was a nurse, explained that if a tiny bit of  something nonsterile gets into the line, it can cause a bacterial shower.  Hers happened w/i 10 minutes or so after chemo.   She shook violently, as if a seizure was taking place, and she became very, very cold.

She was still inside the Infusion Center, so I rushed her back to the Chemo section and she was treated by a chemo nurse, who if I remember correctly gave her Tylenol.   This isn't something that anyone but a chemo medical person should handle though.  

And your daughter should never be alone for several hours after chemo, not just b/c of the potential shower, but b/c it can be so draining.

5.     Her husband should get her affairs in order.   My attorney came to the hospital after initially meeting with my father, sister and I to discuss end of life documents.   She put a rush on them, came back 2 days later and my sister signed in the hospital.  

Out of space.

I’ve read all the responses, which are very very helpful but also fairly depressing. To try something just a bit more cheerful, my mother had breast cancer which also metastasised. She had treatment, and it went into remission for 10 years. She said that those were some of the best years of her life.

Try to help make this time good for your daughter. Knowing that the end may come can help us to appreciate the small good things that somehow manage to crop up most days.

Love and best wishes to you all, Margaret

Ed, I’m just chiming in to say what a huge blessing you were to your wife and now are to your daughter and grandchildren. They all benefit greatly from your love and care. Simply be available as you can, offer to help with what you can, take care of yourself, and enjoy the time with your family. I wish you all the best

I recently went through breast cancer that had not metastasized I was very fortunate. I found the website breastcancer.org very helpful. You will find all sorts of information there. But your best source for information is your daughter.

This is also a great resource
https://www.cancer.org/cancer/breast-cancer/understanding-a-breast-cancer-diagnosis/breast-cancer-hormone-receptor-status.html

Hi!
I'm so sorry to hear about the loss of your wife and now your daughter's cancer diagnosis. You sound like such a caring individual, my heart goes out to you.

My dad was diagnosed with pancreatic cancer in fall of 2020. It's one of the most agressive cancers with a low survivability rate. A year and a half later he's still alive and with a great attitude.

What I can recommend is trying to get the best treatment possible. We live in Orange County, CA. We found out Scripps in San Diego is best for treating tumor cancers out of all of southern California. So even if it's a distance for your family, your daughter may want to get an evaluation there.

My dad when through a round of chemo then went into remission for 9 months and really enjoyed that time. The cancer then came back and he's been going through more chemo. Fingers cross it's looking hopeful that this round is ending soon.

If your daughter ends up going through chemo, have her ask about putting in a port. It's like an implant where the doctors can always draw blood from and insert the chemo drugs without having to stick the patients with a needle everytime. My dad says it's been a life saver because he would otherwise be constantly stuck with needles.

I have a lot of tips for getting through chemo so feel free to PM me or post again if that's what the course of treatment is.

I would suggest trying to keep her spirits up. Same advice goes for her husband. My mom needed just as much cheering up if not more so than my dad. Cancer can be tough on the spouse too. Try to stay positive even when it's difficult. My grandma used to say the power of positive thinking is strong.

Good luck and keep us posted.

DISCLAIMER: I am not a doctor but a breast cancer survivor.

I’m so sorry for the loss of your wife and your daughter’s diagnosis. As I write this, I’m actually sitting at UNC Chapel Hill hospital waiting to see my chemo oncologist for my 6 month checkup following breast cancer in my left breast. I am very lucky as she’s a world-renown doctor that focuses on breast cancer at the Lineberger cancer center.

I had the same type of cancer except I was stage 2; specifically invasive ductal carcinoma. This means cancer cells had breached the milk duct wall and was in my lymph nodes. As for the designations, estrogen/ progesterone positive indicates the cancer feeds off these hormones in the body. HER2 is a protein that is part of regular breast tissue and impacts the rate at which breast cells grow. Negative is better in the grand scheme based on my understanding.

I had a lumpectomy followed by 4 rounds of chemotherapy cyclophosphamide (CYTOXAN), DOCEtaxel (TAXOTERE) and finally 33 rounds of radiation. I lost my hair, appetite and was very fatigued by my 3 round of chemo. I had nausea but only a few bouts of vomiting. Radiation was brutal. The skin was burned off towards the end of treatment and was very painful. Don’t let this scare you. Everyone’s treatment protocol is different.

As a caregiver for my father that had lung cancer before my diagnosis, I say ask your daughter and son-in-law what works best for them in her care and support for the family. I know as her father, you’ll want to do everything you can but you have to also think of your health. You were caregiver to your wife for 10 years and to take on another major role may not be best.

Reading the responses from others, they have great suggestions and mention resources I used. I don’t know if people connect outside of this forum, but I’d be willing to.

My prayers are with you, your daughter and her family.

Cancer care for your daughter will depend on the types of treatment she receives.

Surgery - usual recovery issues of needing help while that side heals and lots of rest.

Chemotherapy - meals, help with housework, lots of rest since she will feel sick and very weak.

Immunotherapy - will probably need lots of rest while her body "learns to kill" the cancer from treatments that teach her body that the cancer is the enemy.

Radiation - lots of rest but not usually feeling sick.

Ask her and her husband how you can be of help.