What Is Squamous Cell Cervical Cancer?

Squamous cell cervical cancer is a malignancy that develops from the thin, flat cells lining the outer surface of the cervix, and it accounts for roughly four out of every five cervical cancer diagnoses worldwide. It is driven almost entirely by persistent infection with high-risk strains of human papillomavirus (HPV), which distinguishes it from many other cancers in that its primary cause is well understood and largely preventable. While the biology is straightforward in outline, the details of how it starts, who it affects, and how treatment has evolved paint a more layered picture.

How Common It Is and Where the Numbers Are Heading

Globally, squamous cell carcinoma (SCC) makes up about 83% of all cervical cancers, far ahead of the second most common type, adenocarcinoma, which accounts for roughly 12%.¹ The rest is a mix of rarer subtypes. The global burden is not evenly distributed: the highest SCC incidence is found in Sub-Saharan Africa, at nearly 30 cases per 100,000 women, compared to much lower rates in high-income countries with established screening programs.¹

In countries with widespread screening, SCC rates have been falling steadily. In the United States, overall cervical cancer incidence has declined at roughly 1.4% per year, driven primarily by declining SCC rates.² South Korea saw an even steeper drop, with its SCC rate falling by more than half between 1999 and 2018.³ Adenocarcinoma, by contrast, has held steady or even risen in some populations, which shifts the proportion of cervical cancers that are non-squamous. The practical takeaway is that screening has been spectacularly effective at catching squamous cell precursors before they become invasive, but less effective at catching the glandular lesions that lead to adenocarcinoma.

The HPV Connection

Virtually all squamous cell cervical cancers trace back to a persistent infection with one or more high-risk HPV strains. The link between HPV and cervical cancer is one of the most thoroughly documented cause-and-effect relationships in cancer biology.⁴ HPV is extremely common; most sexually active people will contract some strain of it at some point. The overwhelming majority of infections clear on their own within a year or two. It is only when a high-risk strain persists for years that cervical cells can begin to transform.

HPV 16 is the dominant player. In one large study of squamous cell carcinomas, HPV 16 was found in about two-thirds of positive cases, with HPV 18 a distant second at roughly 19%.⁵ Women carrying HPV 16 or 18 at initial screening faced an approximately 19-fold increased risk of developing squamous cell carcinoma compared with HPV-negative women, and persistence of HPV 16 infection carried a similar magnitude of risk.⁶ Other high-risk strains like HPV 33, 35, 45, 52, and 58 also contribute, though in smaller numbers.

How HPV Transforms Normal Cells

The virus does not cause cancer overnight. HPV produces two proteins, called E6 and E7, that together dismantle the cell’s built-in safety brakes against uncontrolled growth. E6 targets a protein called p53, which normally acts as a guardian that stops damaged cells from dividing. E6 marks p53 for destruction, removing that safeguard. Meanwhile, E7 attacks another protective protein, pRb, which normally keeps cells from entering their growth phase prematurely. With pRb disabled, cells are pushed into dividing even when they should not be.⁷

Working together, E6 and E7 create a cellular environment where damaged DNA accumulates and cells multiply without restraint. Over years, these changes can progress from mild abnormalities to high-grade precancerous lesions and eventually to invasive cancer. The timeline is typically long: a Dutch modeling study estimated that the median time from a high-grade precancerous lesion to actual cancer was about 23 years, with fewer than 2% of those lesions progressing within 10 years.⁸ That slow timeline is exactly why screening works so well: there is a wide window to catch and treat precancerous changes before they become dangerous.

Where in the Cervix It Starts

The cervix has two types of lining: the outer portion (ectocervix) is covered by squamous cells, while the inner canal (endocervix) is lined by glandular cells. Where these two types meet is called the squamocolumnar junction. This junction is not just a boundary line; researchers have identified a distinct population of cells there with a unique gene-expression profile, thought to be residual embryonic cells.⁹ These junction cells appear to be multipotent, meaning they can develop along different pathways, and they share a molecular signature with over 90% of high-grade precancerous lesions and cervical cancers.¹⁰

This discovery has reshaped how researchers think about cervical cancer’s origins. Rather than cancer arising from any squamous cell on the cervix, the evidence points to these specific junction cells as the likely starting population. Importantly, high-grade lesions linked to cancer-causing HPV strains expressed the junction cell markers at high rates, while lesions linked to low-risk HPV strains rarely did.¹¹ This also has a practical implication: when these junction cells are removed surgically, they do not regenerate, which helps explain why excisional treatments for precancerous lesions tend to be so effective.

Symptoms and When It Gets Noticed

Early-stage squamous cell cervical cancer rarely announces itself with symptoms. When caught by screening, it is almost always asymptomatic. A study from the United Kingdom found that every woman diagnosed without symptoms had stage I disease, while only about 37% of women who presented with symptoms were still at stage I.¹² The most common symptoms when they do appear include abnormal bleeding (after menopause, between periods, or after intercourse) and unusual vaginal discharge. Pain, pelvic heaviness, and urinary or bowel changes tend to arrive later, when the tumor has grown larger or spread to surrounding tissues.

The disparity between symptomatic and asymptomatic diagnosis underscores why screening programs exist. A cancer caught at stage I has a dramatically better outlook than one caught at stage III or IV. Waiting for symptoms means, in many cases, waiting until the cancer has already advanced.

Screening and Diagnosis

Cervical screening has undergone a major evolution. For decades, the Pap smear was the sole tool, detecting abnormal cells shed from the cervix. More recently, HPV DNA testing has been added or substituted, because it catches infections before cells even look abnormal. In head-to-head comparisons, HPV testing was more sensitive overall for detecting precancerous changes, catching about 77% of cases compared to roughly 59% for cytology alone.¹³ For squamous cell lesions specifically, the gap was smaller: HPV testing picked up 75% versus cytology’s 70%, largely because Pap smears are reasonably good at finding squamous abnormalities. The bigger advantage of HPV testing shows up with adenocarcinoma precursors, which are harder to spot on a Pap.

When screening flags a possible problem, the next step is usually colposcopy: a magnified visual examination of the cervix after applying dilute acetic acid, which causes abnormal tissue to turn white.¹⁴ Suspicious areas are biopsied. One study found colposcopy-directed biopsy had an overall accuracy of about 72% when compared to what was found on later surgery, with roughly 88% accuracy specifically for high-grade lesions.¹⁵ Accuracy was best in younger women and when the junction zone was fully visible. In older women or those whose junction zone has receded into the cervical canal, biopsies can underestimate the severity of the lesion, which is why clinicians often combine biopsy results with HPV testing and cytology to make treatment decisions.

Biomarker testing can add another layer of confidence. A dual stain looking for two proteins, p16 and Ki-67, has gained traction as a triage tool. Normally, these two proteins would not appear together in the same cervical cell; when they do, it signals that HPV has deranged the cell cycle. Dual-staining cytology has shown high sensitivity and specificity for identifying high-grade lesions and cancer.¹⁶

Staging

Once squamous cell cervical cancer is confirmed, staging determines how far it has spread and guides treatment decisions. The staging system used worldwide was revised by FIGO (the International Federation of Gynecology and Obstetrics) in 2018 to incorporate imaging and pathology findings. Stage I means the cancer is confined to the cervix, with subdivisions based on how deeply it has invaded and how large it is: stage IB1 covers tumors between 5 millimeters and 2 centimeters, IB2 covers those between 2 and 4 centimeters, and IB3 covers tumors 4 centimeters or larger.¹⁷ Stage II means the cancer has grown beyond the cervix but not yet reached the pelvic wall or lower third of the vagina. Stages III and IV describe progressively more advanced spread, including into the pelvic wall, bladder, rectum, or distant organs.

Treatment

Treatment options depend heavily on how far the cancer has progressed and whether preserving fertility matters to the patient. For very early-stage disease, particularly tiny tumors with shallow invasion, conservative surgery such as a cone biopsy (removing a cone-shaped wedge of the cervix) or a simple hysterectomy with lymph node sampling may be sufficient.¹⁸ For women who want to preserve the ability to have children, a cone biopsy or trachelectomy (removing the cervix while leaving the uterus intact) can sometimes be an option, depending on tumor characteristics.

For larger tumors still confined to the cervix or those with early spread, radical hysterectomy with removal of pelvic lymph nodes has been the traditional surgical approach. Once the cancer has grown beyond what surgery can cleanly remove, or if it has reached the pelvic sidewall, treatment shifts to radiation combined with chemotherapy. Cisplatin-based chemotherapy given alongside radiation became the standard for locally advanced disease after landmark trials in the late 1990s showed it roughly cut the risk of death by 40% compared to radiation alone.¹⁹ This combination remains the backbone of treatment for locally advanced disease.²⁰

Immunotherapy for Advanced Disease

For women with persistent, recurrent, or metastatic squamous cell cervical cancer, treatment options used to be limited and outcomes were poor. That has started to change with the addition of immune checkpoint inhibitors. The most significant advance came from the KEYNOTE-826 trial, which tested pembrolizumab (an immunotherapy drug) added to standard chemotherapy. Among patients whose tumors expressed the biomarker PD-L1, adding pembrolizumab extended median overall survival from about 8 months of progression-free time to over 10 months, and the proportion alive at two years went from about 42% to 53%.²¹

A subgroup analysis of that same trial looked specifically at squamous versus nonsquamous histology. In the squamous cell subgroup with PD-L1 expression, median overall survival reached about 24 months with pembrolizumab versus roughly 14 months with placebo, a meaningful difference.²² Immunotherapy does not work for everyone, and response depends on tumor biology, but it has opened a door that was previously closed for many patients with advanced squamous cell cervical cancer.

Squamous Cell Versus Adenocarcinoma Prognosis

Since adenocarcinoma is the second most common cervical cancer, patients and clinicians naturally compare the two. The evidence here is surprisingly mixed. One surgical study of stage I and II patients found that adenocarcinoma carried a significantly worse prognosis, particularly among stage IB patients who needed postoperative treatment.²³ Another study of patients treated with radiation or chemoradiation found the same pattern: three-year overall survival was about 85% for SCC versus 75% for adenocarcinoma, and this held up across multiple endpoints including pelvic control and distant spread.²⁴

However, one recent analysis that specifically accounted for HPV status concluded that squamous cell carcinoma actually had worse survival outcomes than endocervical adenocarcinoma.²⁵ The discrepancy likely reflects differences in study populations, staging distributions, and whether HPV status was factored in. What is clear is that at equivalent early stages treated surgically and without complicating factors, the two types perform similarly. The differences emerge in more advanced stages and among patients needing adjuvant therapy, where adenocarcinoma tends to respond less well to radiation. The practical lesson is that histologic type matters for treatment planning, but stage at diagnosis matters more for survival than whether the cancer is squamous or glandular.

Prevention Through Vaccination

Because HPV causes the disease, preventing HPV infection prevents the cancer. The HPV vaccine was first tested against HPV 16, and in the initial efficacy trial, zero cases of HPV 16-related high-grade precancerous lesions developed among vaccinated women, compared to 12 cases among those who received a placebo.²⁶ Current vaccines cover multiple high-risk HPV types, including 16 and 18, and are most effective when given before exposure to the virus, which is why vaccination programs target adolescents. Population-level data from countries with high vaccination uptake are beginning to show real-world drops in high-grade cervical lesions among vaccinated cohorts.

Vaccination does not eliminate the need for screening, however. The vaccines do not cover every high-risk HPV type, and women infected before vaccination are not protected against the strains they already carry. Screening remains important as a safety net, particularly for women who were not vaccinated or who were vaccinated after becoming sexually active.

Why the Burden Falls Unequally

Cervical cancer, including its squamous cell subtype, is often described as a disease of inequality. Between 84% and 90% of cervical cancer deaths occur in low- and middle-income countries.²⁷ The reasons are structural: limited access to screening, lower vaccination rates, delayed diagnosis, fewer treatment options, and co-factors like HIV co-infection that accelerate HPV progression. A global analysis found that a modest improvement in a country’s human development index was associated with a 20% decrease in cervical cancer risk and a 33% decrease in mortality, while higher gender inequality independently raised both incidence and death rates.²⁸

This makes cervical cancer somewhat unusual among major cancers: the tools to prevent it, find it early, and cure it at an early stage already exist. The gap is in deploying them. In countries where screening and vaccination are available and accessible, squamous cell cervical cancer is becoming increasingly rare. In countries where they are not, it remains one of the leading causes of cancer death in women. The World Health Organization’s global elimination strategy, which targets 90% vaccination coverage, 70% screening coverage, and 90% treatment access, is explicitly designed to close that gap, and it is achievable because the biology cooperates. Squamous cell cervical cancer develops slowly enough, from a single identifiable cause, through a long precancerous phase, that intervening at any of several points can prevent death.

The Biomarker IMP3 and Predicting Progression

Not every precancerous lesion is destined to become invasive cancer, and clinicians have long sought better tools to distinguish which high-grade lesions pose a genuine threat. One emerging biomarker is IMP3, a protein involved in RNA regulation during embryonic development that gets reactivated in certain cancers. In one study, invasive squamous cell carcinoma was found only in patients whose precancerous biopsies were IMP3-positive; none of the patients whose biopsies tested IMP3-negative developed invasive cancer on follow-up.²⁹ If validated in larger studies, a marker like this could help clinicians avoid both overtreatment of lesions that would never progress and undertreatment of those that would. Alongside the p16/Ki-67 dual stain already in clinical use for triage, these molecular tools are gradually moving cervical cancer management toward more personalized decisions about who truly needs aggressive intervention.