Almost exactly a year ago, I watched Pumarosa flood the cavernous Oval Space in east London with a swell of moody psych rock, heady and hypnotic on the eve of releasing their debut album, The Witch. The rest of the European tour, followed by festivals and a worldwide slot supporting Depeche Mode, was on the horizon. The band were giddy and, after the gig, their friends celebrated by putting on a warehouse party.

“It was great, everyone was going totally wild,” says frontwoman Isabel Munoz-Newsome, picking at poached eggs in a Brighton cafe. But she had been for some tests at the doctor’s a few days before and, at the back of her mind, a tiny voice nagged. Two weeks later, as the album picked up a string of stunning reviews, Munoz-Newsome was diagnosed with cervical cancer.

“I want to talk about it because I’d never had a smear test until then and that’s the only reason I found out,” she says, with quiet urgency. We have spent half an hour chatting about rave culture, small towns, sisters and Patti Smith before she admits awkwardly that the last year of Pumarosa’s success has been the weirdest of her life. “At a time when everything should have been pure magic and everyone was happy and congratulating us, I was so angry. It was surreal. Doing the Jools Holland show and all that stuff, I just thought: ‘What the fuck am I doing here?’”

She had not felt unwell beforehand, but within a month of the diagnosis Munoz-Newsome was operated on and her cervix was removed. “It was pretty gruesome, but [my] womb and everything is still intact, so I’m still getting periods and that’s still functioning, but …” She laughs bleakly. “But getting a smear test every three years is so important.” She can’t emphasise this enough, she says, because she knows so many women make excuses or miss appointments or believe a lack of symptoms means they don’t have to bother; attendance for cervical screenings in the UK was reported in January to be at a 20-year low. “I was so angry at myself that I just hadn’t gone because I was embarrassed. Isn’t that ridiculous? I was embarrassed by my own body. Stupid.”

Munoz-Newsome founded Pumarosa three years ago with her boyfriend Nick Owen, the band’s drummer. The couple left behind the inner-city squat and DIY scene to move to the quieter, outer edges of London last year. She has more space to paint there (the band’s artwork is all hers) and write their songs in a less claustrophobic setting. While the cancer has now gone and she is OK, it has forced her to think about new things and to ask new questions.

“It’s harder to get pregnant,” she says, by way of example. “And once you are pregnant it’s just harder for it to not have complications because you don’t have a cervix. The other thing that was quite weird, which I’d never thought about is: if I do get pregnant, I won’t be able to give birth – it would have to be a caesarean, because [my uterus] is stitched up.” Her hands swoop for emphasis and her chest rises with her voice.

“I’d never considered that I’d never do that thing that’s so primal, and part of me really wanted to; I was super sad about it. When I read that, going through all the implications of the operation, I just broke down. And I was so shocked, because it’s not something I would’ve thought of, and they don’t tell you that stuff at the hospital – I was reading it on the internet, finding out for myself.” She didn’t know beforehand? “They don’t tell you,” she shrugs.

Munoz-Newsome’s mother is an artist who marked the birth of her elder daughter with an extensive photography project. “The whole of my birth is documented in photos. And when I was little we weren’t allowed to watch scary movies, so we’d look at that album. It’s really progressive and really radical and they’re beautiful photos, but we just thought: ‘Blood! Eurgh!’” She laughs, softening the stiff irony hanging in the air.

Munoz-Newsome grew up in Bath with her sister, Fernanda, in a spirited, creative household; their Chilean father is an illustrator and their mother now lectures part-time in fine art. Both daughters moved to London for art school: Fernanda has become a dance artist and something of a muse to her sister; Isabel studied theatre design and helped create sets for plays in pub theatres and the National before music became full-time.

“Fernanda is a big point of gravity in my life, I suppose – loads of stuff revolves around her. Even without realising it.” The two share circles of friends and explored London’s hedonistic elements together in their 20s.

Priestess, the seductive lead single from The Witch, was inspired by her sister’s performances, with a nod to Victorian occultism and pagan folklore. The concept of the album itself came via a copy of Silvia Federici’s cult Marxist-feminist text, Caliban and the Witch, which Isabel had borrowed from Fernanda.

“It’s an incredible piece of work about the transition from feudalism to capitalism from the female perspective,” she says. Federici centres on the dark saga of the 15th-century witch hunts that consumed Europe with terror for more than 200 years; the book challenges the idea that capitalism was a progressive or necessary development by revealing its reliance on spectacular violence against women.

“It was just completely eye-opening to read that, prior to that, women had actually occupied quite a different place in society in England, France, Italy. They were metalworkers, they worked in fields and were strong – we are strong – and men did lots of things that have now come to be traditionally seen as women’s work. The idea that the church was at one point setting up more and more brothels to push the idea of the woman as a whore is mindblowing, but learning it as a woman is so powerful – it’s freedom.”

The book became a source of energy for her, she explains; it also inspired the band’s current single, Lions’ Den. “It’s empowering to realise that this isn’t just the natural order of things, it didn’t naturally occur – it was horrifically pinned on us. Men, too.”

Federici writes about the multiple ways women have been vilified in history, “accused of being unreasonable, vain, wild, wasteful”. “Especially blamed was the female tongue, seen as an instrument of insubordination,” Federici argues. The tropes of the disobedient wife, the witch, the shrew, pervaded popular culture of the period; Shakespeare’s works could be read as a manifesto of the age.

Munoz-Newsome is beguiling on stage – all limbs and joyful abandonment – but enthusiastic, unpretentious company. She talks about growing up in love with “tacky dance music like Baby D, N-Trance, fairground music”, grateful that Somerset felt a less self-conscious place to be a teenager, compared with the capital. The night before we meet, the band play a sellout show in Brighton to a largely male audience. Today, they have been announced on the bill for Robert Smith’s pleasingly doomy but inescapably blokey Meltdown. How does she feel about the way she is inevitably objectified as ‘the sexy frontwoman’?

“It’s strange,” she admits. “When you’re a teenager, that’s all you want, so you kind of have to try and enjoy it. Last night felt fine, the energy was nice, but occasionally it’s gross and there are certain gigs where I feel I’m responding to it on stage but don’t feel so good afterwards.” Munoz-Newsome catches herself sometimes, uncomfortable at the pressure to look the part of the enigmatic, beautiful, blond waif. “It would be so much cooler just to be, like: ‘Fuck this.’ But I’ve always loved dressing up and playing with costumes; I don’t want to limit that for myself. Earlier on, I was more conventional in what I was trying to do and it was boring.”

Ultimately, women are conditioned to worry about the way they look. “Yes. It’s like having a radio on in the back of your head all the time saying something that’s completely unintellectual and not very interesting, but you can’t help listening to it.” We come back to Federici: “It’s just a symptom of capitalism; apparently, women spend something mad like up to 30% of their income on their appearance. There’s a huge industry playing on our insecurities. It’s disgusting.”

Outside, a jagged wind and rain whip against the cafe windows. It is resolutely gloomy, but Munoz-Newsome is sanguine. “I used to be quite obsessive with certain things to do with the band and so anxious about not being exploited as a woman and as artists – that’s just the way the industry has been set up – but I can’t worry about it any more,” she says. The shock of cancer hasn’t changed her outlook, but it has offered perspective. “Now I find a way to constructively get over [anxiety] – when I feel it creeping up, I just think: ‘Breathe! And do something else.”

Pumarosa play Meltdown festival at the Queen Elizabeth Hall on 23 June. Their new single, Lions’ Den, taken from the album The Witch, is out now