Her doctor said that the biopsy to the lung is risky. So, without the biopsy to the lung, she is given further hormone therapy, and when it doesn't shrink the growth, the doctor advise for chemo therapy.

I have a few questions :
1). If biopsy is risky, what type of risk ? Is it fatal ? (This is really my main question, because I feel that without knowing whether it is cancer / which type of cancer, the treatment could be futile...)
2). Is chemo therapy same for breast cancer or lung cancer ?
3). Is it that if there is a lump in the lung, it is cancer ? Can it be something else ?
4). Is it a spread from the previous breast cancer or primary lung cancer ?
5). Is it true that when you have one cancer, it will be most likely the spread of the previous cancer, instead of a new primary cancer ?
6). I have heard that if it is a spread from the breast cancer, it is likely to appear in more than 1 lump in the lung, and it is likely to spread to the liver, too. Is it true ?

-There is a risk of bleeding. If this is not controllable this can lead to death through exsanguination (blood is pumped into the lungs/bronchi outside the blood vessels) and/or suffocation by the same mechanism. In centers with modern equipment and experienced radiologists this risk is small.

Depends on what type of lung cancer it is. An adenocarcinoma would respond to most if not all of the typical breast cancer chemo, the other tumor types not.

Did your aunt smoke? If not, this is more likely to be a metastasis of the breast cancer. Check the tumor markers for breast and lung. The treatment with hormones (tamoxifen I assume) is also a good idea if your aunt is old and a biopsy or operation is too risky.

-The biopsy of suspicious lung nodules is relatively routine. There are risks which vary with individual patient dependent on lung function. There are many factors which play into this decision. However the standard for a solitary tumor in the lung in a reasonably healthy person is to pursue histological diagnosis by cytology or biopsy via bronchoscopy or CT guided needle biopsy.

I would not count on this being a breast carcinoma metastasis. The chance of it being a lung cancer is increased if there is a history of smoking. An early stage lung cancer is potentially curable and your aunt might miss that chance if she is being treated with tamoxifen which will have no effect on lung cancer.

Consider getting a CT scan of the chest and abdomen. If she has multiple lung tumors or liver tumors then this is likely breast cancer and Tamoxifen would be appropriate. If she has only one lung tumor then I would consider getting a diagnosis.

The possibility exists that her physicians believe she is in poor health and would not tolerate the biopsy or an aggressive therapy if indeed she had a stage I lung cancer. If she is unwilling or unable to tolerate a thoracotomy or radiation therapy then it probably is not worth pursuing a biopsy.