Breast Cancer Explained: From Cell Change to Treatment

Two patients can both tell you they have breast cancer. Their tumours might even be roughly the same size. Then you look at their treatment plans and they are completely different.

That is one of the things that can make breast cancer confusing at first. The words breast cancer tell you where the cancer started, but they do not tell you exactly how that cancer is behaving. To make sense of the treatment plan, you need to know a bit more about the cells themselves, whether the cancer has travelled anywhere else and whether those cells carry targets that treatment can use.

So rather than trying to memorise a list of breast cancer treatments, start with a normal breast cell and follow what changes.

From a normal breast cell to an invasive cancer

The breast is made up of lobules, ducts, connective tissue, fat, blood vessels and lymphatics. The lobules can produce milk and the ducts carry it towards the nipple. Most breast cancers are carcinomas, meaning they begin in epithelial cells associated with these structures.

Normally, cells do not just keep dividing forever. Their growth is controlled, damaged DNA can be repaired and cells that are no longer needed can undergo programmed cell death. Cancer develops when molecular changes begin to disrupt those controls. An abnormal cell survives when it should not, continues dividing and passes those changes on to the cells that come after it.

This is not usually one switch suddenly being flicked. Over time, a group of abnormal cells can gain more of the characteristics that allow a cancer to grow, survive and eventually invade nearby tissue.

This is where ductal carcinoma in situ (DCIS) and invasive breast cancer start to make sense. In DCIS, abnormal cells are sitting within the duct system but have not invaded through the basement membrane into the surrounding breast tissue. They are abnormal, and DCIS is treated because some cases can progress to invasive cancer, but DCIS itself is not the same thing as invasive breast cancer.

Once malignant cells cross that boundary and enter the surrounding tissue, the cancer is invasive. That matters because those cells now have access to the tissue around them as well as lymphatic and blood vessels.

Think about the axilla for a moment. Much of the lymph from the breast drains towards the axillary lymph nodes. Suddenly all those notes about sentinel lymph-node biopsy and axillary nodes make more sense: the team is interested in whether cancer cells have travelled into the regional lymphatic system.

One important distinction here: an involved axillary lymph node does not automatically mean stage 4 breast cancer. Regional nodal disease and distant metastatic disease are not the same thing. Metastatic breast cancer means the cancer has established disease at a distant site, commonly including bone, liver, lungs or brain.

Before any of that can be worked out, though, the patient usually arrives because something has prompted assessment. That might be a new breast or axillary lump, a change in breast shape, skin dimpling, nipple inversion, a nipple or skin change or unexpected nipple discharge. None of those findings can diagnose cancer by themselves. Benign breast conditions can cause changes too, which is why the next step is proper assessment rather than guessing from what something looks or feels like.

When you see breast investigations on placement, it helps to ask what each one is actually trying to tell us. Clinical examination gives information about what can be seen and felt. Mammography and ultrasound help locate and characterise an abnormality, and ultrasound can also be used to assess the axilla and guide sampling. A core biopsy is different because it gives the pathology team actual tissue to examine.

A useful way to remember it is this: imaging can show us the abnormality; the biopsy helps tell us what the abnormality actually is.

The results then have to be put together. The team considers the breast lesion, the axilla, the histology, the grade and the receptor profile alongside the wider clinical picture. Not everyone with a newly diagnosed early breast cancer needs exactly the same staging scans. Further imaging depends on what the team already knows and whether there is concern about more extensive disease.

Why two breast cancers can lead to completely different treatment

This is the bit that unlocks a lot of breast cancer terminology. You will hear type, grade, stage and receptor status in handovers and MDT discussions. They are not four ways of saying the same thing.

Type describes what kind of breast cancer the pathologist is looking at. Grade is about what those cells look like and gives information about how biologically aggressive the cancer appears. A higher grade generally means the cells have more aggressive features. It does not tell you how far the cancer has travelled.

That is the job of stage. Stage is about the anatomical extent of the disease, taking into account the primary tumour, regional lymph nodes and whether there is distant metastasis. This is why “small tumour” and “early-stage cancer” are not interchangeable. Size matters, but it is only one part of the picture.

Then comes receptor status, and this is where treatment starts to feel much less random. In invasive breast cancer, the pathology team assesses oestrogen receptor (ER), progesterone receptor (PR) and HER2 status. These results tell the team something about the biology of that particular tumour and, importantly, whether there are useful treatment targets.

Take an ER-positive cancer. If the cancer cells are using oestrogen signalling to help drive growth, endocrine treatment can interfere with that pathway. That is why medicines such as tamoxifen or an aromatase inhibitor can make sense for one patient but would not simply be given to everybody with a breast tumour.

HER2 is another growth-signalling receptor. Some breast cancers have increased HER2 activity. If HER2 is helping drive the cancer, it can also give the oncology team something to target with HER2-directed treatment.

Then you might hear triple-negative breast cancer. This means the cancer does not have the ER, PR or HER2 targets used to define those subtypes. It does not mean there is no treatment. It means endocrine therapy and HER2-directed treatment are not useful in the same way, so the treatment plan is built around other features of the cancer. Chemotherapy is important in many pathways, and immunotherapy is used for selected patients where the cancer and the person's circumstances meet the relevant criteria.

Now put two patients side by side. Both have an invasive tumour measuring about 2 cm. Patient A has a lower-grade, ER-positive, HER2-negative cancer and no detected nodal involvement. Patient B has a higher-grade, HER2-positive cancer with involved axillary nodes.

On paper, “2 cm breast tumour” sounds similar. Clinically, these are not the same cancer story at all. The biology is different, the nodal picture is different and the treatment options are different. That is why trying to predict someone's treatment from tumour size alone will get you into trouble.

This is also what the breast MDT is actually doing. They are not looking at the words “breast cancer” and picking a treatment from a standard list. They are bringing together the pathology, receptors, extent of disease, the patient's general health, likely benefits and harms of treatment and, importantly, what the patient wants.

If the disease can be treated locally, surgery may involve breast-conserving surgery or mastectomy depending on the cancer and the person's circumstances. The axilla may need staging or treatment too, for example with sentinel lymph-node biopsy or other axillary surgery.

Radiotherapy is a local treatment as well. After breast-conserving surgery, it is commonly used to reduce the risk of cancer returning in the remaining breast tissue. It can also be recommended after mastectomy in selected patients where the risk of local recurrence is higher.

Then there are the systemic treatments, which work beyond the breast itself. This is where two words students often see in the notes are worth understanding properly. Neoadjuvant treatment is given before definitive surgery. It may reduce tumour burden, sometimes make breast-conserving treatment possible and can show how the cancer responds to treatment. Adjuvant treatment comes after surgery and aims to reduce the risk of microscopic disease later causing recurrence.

So the pathway is not automatically “diagnosis, surgery, chemotherapy”. Some patients have systemic treatment before surgery. Some need chemotherapy and some do not. Hormone-receptor-positive disease may have an endocrine treatment option. HER2-positive disease may have a HER2-directed option. Immunotherapy is relevant to selected cancers rather than breast cancer as a whole.

When breast cancer has spread to distant sites, the aim of treatment changes. Metastatic disease is usually managed with systemic treatment aimed at controlling the cancer, prolonging life where possible, managing symptoms and protecting function and quality of life. The biology still matters here too. If breast cancer recurs, receptor status may be reassessed when a change would affect treatment, because the biology of recurrent disease can influence what the team does next.

If you get lost in the terminology, come back to this: What type of cancer is it? What does the grade tell us? Where has it spread? What receptors are present? What does all of that mean for this particular patient?

Now bring all of that back to the patient

Understanding the pathology is useful, but on placement you are much more likely to meet the consequences of the cancer and its treatment.

Imagine you are looking after someone the morning after breast surgery. “Breast cancer, post-op” is not enough information to guide your care. What operation did they have? Was there axillary surgery? Do they have a drain? What does the wound look like? How is their pain? Are their observations where you would expect them to be? Has anything changed since the last set of observations?

Increasing swelling, bleeding, worsening pain, signs of infection or unexpected deterioration need review. A seroma, a collection of fluid in the surgical space, can develop after breast or axillary surgery. Your job as a student is not to independently decide how that should be managed. Your job is to notice what is happening, assess within your competence, communicate it and involve the right person.

Axillary surgery also helps explain why lymphoedema comes up so often in breast cancer care. If lymphatic drainage has been disrupted, swelling can develop in the affected arm or nearby tissues. The useful nursing lesson is not a list of blanket lifelong rules. Listen to what the patient is noticing, look for swelling or skin problems, reinforce the advice given by the specialist team and escalate concerns.

Now imagine the patient is on systemic anticancer treatment instead. “On chemo” still does not tell you enough. Which treatment? Which cycle? When did they last receive it? What symptoms have appeared since then?

Chemotherapy can cause myelosuppression, nausea, mucositis, fatigue, appetite changes, neuropathy and other toxicities, but regimens differ. Endocrine treatments bring a different set of effects. HER2-directed treatments have their own monitoring requirements. Knowing the actual treatment makes the patient's symptoms much easier to put into context.

One situation you should never shrug off is a patient receiving systemic anticancer treatment who becomes acutely unwell. Treatment can cause neutropenia, and suspected neutropenic sepsis is a medical emergency. You do not need to prove that the patient has neutropenic sepsis before you escalate. If they are receiving anticancer treatment and are suddenly unwell, assess within your competence, follow the local pathway and get senior help promptly.

The same thinking applies to other red flags. New severe breathlessness or pleuritic chest pain should not automatically be written off as “probably treatment”. New neurological symptoms, weakness, altered sensation, severe or changing headache or new bladder or bowel dysfunction need urgent assessment. Severe or changing back pain with neurological features is especially important because metastatic spinal cord compression is an oncological emergency.

And breast cancer nursing is not just observations, wounds and treatment toxicities. The diagnosis can affect body image, sexuality, fertility, menopausal symptoms, relationships, work and how somebody sees themselves. Two people can have the same operation and feel completely differently about it. A mastectomy is not just another line in the surgical history, and breast-conserving surgery is not automatically emotionally easier.

This is where talking to the patient matters. What are they worried about? What have they understood about the plan? Are they worried about how their body will look, going home, caring for children, work, fertility, sex, recurrence or something completely different? Do not decide which concern they should have.

Privacy matters too. Breast examination, wound care and conversations about body image can feel exposing. Explain what you are doing, gain consent, protect dignity and know when the breast clinical nurse specialist or another member of the MDT needs to be involved.

If a patient asks, “What stage am I?” or “Why am I getting this treatment?” and you do not know their individual oncology plan, do not fill the gap with a generic answer. Help them get the right answer from the registered nurse, breast clinical nurse specialist or oncology team.

And when you hand the patient over, try not to stop at “breast cancer, post-op, stable”. Tell the next nurse what has actually happened: the procedure or treatment, when it happened, current observations, pain, wound and drain status if relevant, mobility, treatment-related symptoms, psychosocial concerns, what has changed and what the plan is.

That is really the point of understanding the pathophysiology. You are not learning ER, HER2, lymph nodes and staging so you can recite them. You are learning them because they help you understand why this patient is having this treatment, what might happen next and what you need to notice while you are caring for them.

The Bleepbook version to remember: abnormal cells stop following the normal rules → invasive cells cross into surrounding tissue → cancer may reach lymphatics or the bloodstream → pathology tells us what sort of cancer we are dealing with → staging tells us how far it has gone → the MDT uses all of that, alongside the patient, to decide what happens next.

References

National Institute for Health and Care Excellence (NICE). Early and locally advanced breast cancer: diagnosis and management (NG101). Available at: NICE NG101.

National Institute for Health and Care Excellence (NICE). Advanced breast cancer: diagnosis and treatment (CG81). Available at: NICE CG81.

National Institute for Health and Care Excellence (NICE). Neutropenic sepsis: prevention and management in people with cancer (CG151). Available at: NICE CG151.

National Institute for Health and Care Excellence (NICE). Spinal metastases and metastatic spinal cord compression (NG234). Available at: NICE NG234.

NHS. Breast cancer in women. Available at: NHS breast cancer information.

Nursing and Midwifery Council (NMC). The Code: Professional standards of practice and behaviour for nurses, midwives and nursing associates. Available at: NMC Code.