Nos, or NOS, stands for Not Otherwise Specified. It is terminology that is used in the ICD-9-CM coding classification system that is used by the Health Information Management Department for generating hospital bills for payment by patients and insurance companies and for statistical reporting information sent to Medicare. The doctor is writing this thinking that he is helping the medical coders in the Health Information Management Department or Medical Records.
NEC is also an ICD-9-CM term that means Not Elsewhere Classified. Again, it really contributes nothing to the medical diagnosis as you will work with it. It is a medical coding term.
You will probably never see an ICD-9-CM coding manual in your whole career of nursing. This is something that is used by medical records or health information management departments. Coders convert medical diagnoses into standard code numbers that are recognized throughout this country by Medicare, Mediaid, and every single medical insurance company.
ASCVD stands for Arteriosclerotic Cardiovascular Disease.
I suspect your "malign neople breast nos" stands for malignant neoplasm of the breast, nos. In simple terms its a malignant or cancerous tumor of the breast and that's all he can say about it at the time he wrote that.
Let me recommend a supplemental little paperback that might be helpful to you. It is called Medical Abbreviations: 15,000 Conveniences at the Expense of Communications and Safety, by Neil M. Davis. I have the tenth edition and it has 22,000 medical abbreviations in it. I think the 12th Edition is the one currently in print. I got mine from Barnes and Noble by ordering it on their website. Docs love to abbreviate stuff, especially different diseases and disorders and most of them are listed in this book.