The many lives of breast cancer: understanding rare subtypes

Conversations about breast cancer usually bring up a single picture in one’s mind: a woman feels a lump, gets it tested, is told she has breast cancer, and then follows a pathway of surgery, chemotherapy, radiation and hormone tablets. That picture is almost always based on the commonest form of the disease – what the World Health Organization now calls “invasive carcinoma of no special type” (NST), formerly known as invasive ductal carcinoma. Around 70–80% of invasive breast cancers fall into this group.

But breast cancer is not one disease. Under the microscope, it is a family of diseases that all happen to arise in the breast. Some are aggressive, some are surprisingly gentle, some have not yet turned into true cancer, and some occur in groups we rarely talk about, such as men. The subtype of breast cancer in the pathology report can change the likely behaviour of the disease and the kind of treatment it needs.

In India, where breast cancer has become the most-commonly diagnosed cancer among women in many urban registries, these rare forms are not a side-show: they are part of the everyday reality of oncology.

Why subtype matters

Once a lump is detected on examination or imaging, the next crucial step is tissue diagnosis. In modern practice, this is usually done on small samples taken with a core needle biopsy. The pathologist then studies thin slices of this tissue under the microscope and performs special stains to look for hormone receptors and other markers.

From this process comes the pathological diagnosis. It tells us: whether there is cancer at all, where it seems to have started (ducts vs lobules), what pattern the cells form, and whether they express oestrogen, progesterone or HER2 receptors.

Two women may both hear the words “you have breast cancer” but have very different diseases under the microscope. At this stage, communication between the radiologist, pathologist and surgeon is indispensable. The image, the biopsy and the clinical examination must all make sense together, especially when the pattern is unusual. This is why multidisciplinary breast units – where these specialists work together – are important to manage rare types safely.

When there is no neat lump

The most important non-ductal subtype to understand is invasive lobular carcinoma (ILC) – the second-most common kind of invasive breast cancer, accounting for roughly 1 in 10 cases. It begins in the lobules – the milk-producing glands – rather than the ducts. Under the microscope, ILC cells tend to line up in single files, slipping between normal structures instead of clumping into a ball. This microscopic pattern creates some very practical differences.

Compared to usual ductal cancer, ILC: may not form a well-defined lump that is easy to feel, can make the breast feel generally fuller, heavier, or slightly firmer in one area, may cause subtle pulling in of the skin or nipple rather than a distinct nodule, and can be harder to pick up on a mammogram, because it sometimes blends in with normal tissue.

Most ILCs are hormone-receptor positive, which means they respond well to anti-oestrogen tablets given for several years after surgery. Long-term outcomes can be very good when the disease is caught early. The challenge lies in recognising the disease early, both for women, who may not feel a classic lump, and for clinicians, who must be alert to more subtle changes.

The key message is that breast awareness is not just about “feeling a lump”. If one breast slowly begins to look or feel different from the other – in size, shape, firmness or texture – and those changes don’t go away, it is worth getting checked, even if you cannot point to a discrete lump.

The gentler outliers

Not all special subtypes of breast cancer are very dangerous. Some are biologically gentle and, when detected early, can be controlled remarkably well with relatively modest treatment.

A group of these “good outcome cancers” includes tubular carcinoma, colloid (mucinous) carcinoma, and adenoid cystic carcinoma.

Tubular carcinoma is made up of tiny, well-formed tube-like structures. These tumours are usually small, slow-growing and respond very well to treatment. Mucinous (colloid) carcinoma produces pools of mucus in which cancer cells appear to float. This form often occurs in older women and tends to behave less aggressively than typical NST cancers. Adenoid cystic carcinomas of the breast are rare tumours with a distinctive cribriform pattern; they are often low-grade and less prone to spread to lymph nodes.

In many women with these subtypes, disease can be effectively controlled by first-line surgery and anti-oestrogen tablets, without the need for intensive chemotherapy. Despite being “rare”, these cancers are immensely treatable, provided they are recognised in time and managed with due care.

The aggressive subtypes

At the other end are subtypes that tend to behave more aggressively. Among these are invasive micropapillary carcinoma and metaplastic carcinoma.

In micropapillary carcinoma, the cancer cells form clusters that seem to float in empty spaces under the microscope. This pattern is strongly associated with a higher risk of lymphovascular invasion and lymph node spread. Even when the primary tumour in the breast is not very large, the nodes can be significantly involved. Recognising this pattern alerts the treating team to the need for careful axillary assessment and appropriate systemic therapy.

Metaplastic carcinoma is rarer but particularly important. Here, the tumour contains areas where the cancer cells have transformed into forms that resemble bone, cartilage or spindle-shaped connective tissue. These tumours often present as rapidly enlarging, firm lumps, are more likely to be triple-negative (lacking ER, PR and HER2), and can be less responsive to standard chemotherapy compared to ordinary NST tumours.

Outcomes for these aggressive subtypes depend heavily on stage at diagnosis and access to expertise. These tumours underscore once again how crucial accurate pathology and multidisciplinary planning are, to achieve good outcomes in breast cancer.

When the lump keeps growing

While all the tumours discussed so far are unequivocally cancers, phyllodes tumours are somewhat different. They arise from the fibrous and glandular tissue of the breast and are classified as benign, borderline, or malignant based on their microscopic features, depending on how active and abnormal the stromal component appears. They are, in other words, tumours of the breast, but not breast carcinoma in the usual sense. Under the microscope, they have a leaf-like architecture, which is where the name “phyllodes” comes from.

Clinically, a phyllodes tumour typically presents as a smooth, mobile lump, which at first glance can resemble a common fibroadenoma (a benign breast lump) and then begin to grow quickly, sometimes over just a few months.

In countries like India, where women may delay seeking care because of fear, stigma or distance, it is not unusual to encounter phyllodes tumours that have been allowed to reach very large sizes.

Unlike typical breast cancers, phyllodes tumours rarely involve the lymph nodes, so routine removal of nodes is often unnecessary. The mainstay of treatment is surgical excision with a rim of healthy tissue around the tumour, to reduce the risk of it coming back in the same area. Malignant phyllodes tumours, however, can spread through the bloodstream, most commonly to the lungs.

If you have been told you have a “fibroadenoma” or a “benign lump”, but it keeps increasing in size or returns quickly after a minor operation, it is worth asking your doctor if a phyllodes tumour has been ruled out by proper pathology.

Male breast cancer

Finally, there is a group that is rare not because of the tumour type, but because of who it affects: men. Public campaigns about breast cancer overwhelmingly depict women. Yet men have breast tissue too, and they can also develop breast cancer.

Warning signs in men are similar to those in women: a firm lump behind or close to the nipple, nipple retraction, ulceration or crusting, discharge or bleeding from the nipple, and occasionally a lump in the armpit.

Risk factors can include increasing age, a strong family history of breast or ovarian cancer, certain inherited gene mutations, hormonal imbalances, and prior radiation to the chest.

The most important step is the first one: recognising that a breast lump in a man is not something to be ignored, but something to be examined. For men who are affected, the experience can be doubly isolating. Many have never heard of male breast cancer before their own diagnosis and some delay seeking help because breast cancer is perceived as a “women’s disease”. Treatment follows the same broad principles as in women – surgery, hormone tablets for hormone-receptor–positive disease, and chemotherapy or targeted therapy where indicated. When diagnosed early and treated appropriately, male breast cancer can usually be brought under good control.

What to watch for?

No one can tell the subtype of a breast lesion by touch alone. That is the work of imaging and pathology. But there are certain patterns of change that should never be ignored or endlessly reassured away:

• Any new lump in the breast or armpit that persists beyond a few weeks, in women or men.

• A known “benign” lump that suddenly begins to grow faster.

• One breast becoming noticeably different in size, shape or firmness compared to the other.

• Nipple changes – new inversion, distortion, crusting, or discharge, especially if blood-stained or from a single duct.

• Skin changes – such as persistent thickening or dimpling – that do not settle.

Most of these will turn out to be benign. Some will be common NST/ductal cancers. A small minority will be the rarer entities described above. For all of them, timely evaluation including imaging, core needle biopsy, and expert interpretation is far better than months of waiting and watching.

A test of systems

Rare breast cancer subtypes are a quiet test of our systems. They ask whether radiologists, pathologists and surgeons are talking to each other; whether multidisciplinary care is available beyond a few big cities; and whether our registries are capturing the full spectrum of disease, not just its most familiar face.

For all of us, the message is simple: breast cancer is not just one story. There are many variations – some gentle, some more demanding – but all of them are very treatable when found early and approached without fear or delay. Paying attention to the quiet signals that something is different, and acting on them, remains the most powerful step we can take.

(Dr. Nisha Hariharan is a consultant breast cancer specialist and oncoplastic surgeon, and a Global Fellow, WomenLift Health, based out of Hyderabad. dr.nishahariharan@gmail.com)